1. Measurements were made of the head length, head width, total body length, antenna length, length and breadth of 3rd antennal segment of head and body lice from natural infestations. In all measurements (except the last) the means were significantly different for. the two forms, but in all cases there was considerable overlap.

2. Head lice reared continuously on the body for forty-three generations (over 2 years) did not change systematically in size. Body lice reared under similar conditions were likewise constant.

3. There was a highly significant difference between mean measurements of all the samples of head lice reared for up to 2 years on the body when compared with body lice reared for a similar period in the same way. The means for lice worn 24 hr. per day were less than those worn 12 hr. per day in both strains. An experiment showed that this is probably due to a difference in average temperature.

4. The mean live weights of head and body strains were even more distinct than linear dimensions on the several occasions when these were recorded.

5. Measurements of the dimensions of the opercula of the eggs of the two races and the numbers of air cells in them were distributed in the same way as the body measurements: that is, distinct means but overlapping individuals.

6. Ventral abdominal muscles in wild head lice are typically confined to segment 5. (The forty specimens examined adhered to this rule.) In wild body lice, muscles are usually also present in segment 4 as well.

7. Hybrids (female body x male head louse) were fertile for several generations. In size, the F1 generation was intermediate, but the F2 and F3 generations became identical with the body louse strain.

8. Eggs of the body louse strain hatched at the same time as those of the head strain, but the body strain reached a significantly higher percentage hatch.

9. The times of moulting during development were studied in both races in relation to differing opportunities to feed (24, 12, 6 and 3 hr. per day). The two strains showed very similar reactions in regard to speed of development, but throughout there was a higher pre-imaginal mortality in the head strain.

10. Head lice were shown to be considerably more susceptible to starvation than body lice.

11. If adults of the two strains are mixed, there is no tendency towards homogeneous mating. Of the mixed matings, those between body louse males and head louse females are much more common than the reverse.

12. Female head lice show a slight difference in their egg-laying preferences when offered a choice of hair, voile and tape.

My thanks are due to Prof. P. A. Buxton, F.R.S., for a number of helpful suggestions based on his extensive knowledge of louse biology and to Dr J. O. Irwin for critical comments on the statistical issues.

By employing a combination of sub-stage heating and supra-vital staining with eosin or neutral red it was found that viable and non-viable hydatid scolices could be distinguished microscopically. Using this technique a study of the effect of heat in vitro on hydatid scolices has shown that death resulted from exposures at 50° C. for 70 min. and at 55° C. for 30 min.

Experiments on the effect of boiling in destroying the contents of fertile cysts embedded in sheep liver showed that when offal was added directly to boiling water destruction of scolices was complete after 40 min. boiling. When the infected liver was placed in cold water brought to the boil, scolex death was assured only after 30 min. subsequent boiling.

Ultra-violet radiations of 2537 A. did not kill scolices under the conditions adopted. Although this wave-length would apparently be ineffective as a scolicicidal agent in surgery of the human hydatid cyst, irradiation of hydatid fluid containing scolices might offer a simple method for initial sterilization of scolex culture media.

The author wishes to acknowledge many helpful suggestions and loan of the Hanovia lamp by Dr G. M. Richardson of the Virus and Immunology Research Department, Otago Medical School.

The material described in the present paper was collected by Dr Rašín in 1935. It consisted of an infected ovary of Leuciscus cephalus L. from the Svitava river near Brno, and an ovary of Esox lucius from Ríčka in the vicinity of Vranovice near Brno, C.S.R. The ovaries were fixed partly with formol-Zenker solution, and partly with Gilson's fixative. The infected roes could be distinguished easily from the healthy ones by their white colour. Histological examination showed that they were infected with Microsporidia. As the material had been fixed, no polar filaments could be observed. Sections, 4μ in thickness, were stained with Heidenhain's iron haematoxylin, which once more proved to be a stain which gave the greatest contrast in preparations of Microsporidia. In addition, sections were stained with Mallory and Mann's stains, and were also subjected to Feulgen's nucleal reaction.

1. The number of third stage larvae of Trichostrongylus retortaeformis on different portions of herbage was studied. Three plant-types were used: Festuca sp., Clover, and Carex sp.

2. On Festuca spp., 5·5 in. in height, 90% of the total number of larvae occurred on the lower 3 in. of the blades; 50% occurred on the basal 1·5 in. On the same species, 3 in. high, 90% were found on the lower inch. This showed that the distribution on the blades was not limited by the total distance the larvae were able to travel. Nor was it limited by the rate of movement, because the form of the distribution was not altered after 3 days.

3. Larvae were found to be evenly distributed vertically over the stems and leaves of clover.

4. On Carex vulgaris 10 in. high the larvae were limited to the lower 2 in.

5. The distribution of larvae in the soil, ‘mat’ and herbage was recorded monthly throughout the year. During the warmer months of June, July and August the majority of larvae were found on the grass blades, and more larvae occurred in the soil than in the ‘mat’. During September, October, April and May more larvae were found in the ‘mat’ and fewer were found on the blades and in the soil. From November to March nearly all the larvae occurred in the ‘mat’. From December to January no larvae were found on the grass blades or in the soil.

6. Climatic conditions in the herbage were studied.

7. It was shown that the temperature below the top of grass blades may differ considerably from the air temperature. Differences of 10° F. were recorded between the tips and bases of grass blades. In general, there was a gradient of temperature established between the upper and lower parts of the grass.

8. High humidities occurred in the lower parts of the grass, even when atmospheric humidity was low. The relative humidity at the tips was never higher than that at the base of the blades.

9. The rate of evaporation decreased towards the base of the blades.

10. The light intensity decreased towards the soil. Midway between the top of the grass and the soil the light intensity fell rapidly.

11. The height, density and type of herbage modified the effect of the climatic factors.

12. It was concluded that the vertical distribution of larvae could be explained without reference to geotropism and that most of the larvae occurred in that portion of the herbage in which there was least climatic change.

The writer wishes to thank Prof. A. D. Hobson for advice and criticism and Mr W. Lyle Stewart, M.R.C.V.S., for encouragement and the provision of facilities, and Dr G. Lapage for helpful criticism and advice in the preparation of the MS. Thanks are also due to King's College, University of Durham, for a grant from the College Post-Graduate Research Fund.

On the whole published data on the host relationships of Ixodes ricinus L. in Britain are rather inadequate, but the following points emerge:

The tick (stages unspecified) has been found on twenty-three mammal, twenty-one bird and one reptile species. These include both wild and domestic animals. There are no records of non-hosts. The host list is incomplete. Its length and variety suggest, however, that the tick will feed on practically any mammal or bird it may meet.

Tick stages found on fifteen mammal, twenty-one bird and one reptile species have been recorded. For a number of reasons (see text) ‘recorded’ absence of any tick stage from an animal is not necessarily reliable. This, together with the incompleteness of the host list, detracts a little from the assertion of several authors, namely, that in general larvae and nymphs occur on both mammals and birds, but adult ticks on mammals only.

No precise host-potentials for any wild species relative to sheep (or other important farm stock) have been published in Britain. But, in one area, Scottish mountain hare, red deer and roe deer have been slaughtered on a large scale because of their alleged importance as hosts. Very inadequate data from two authors seem to suggest that as normally stocked populations (a) grouse are negligible compared with sheep as hosts to female ticks, and (b) mountain hare and red deer may play quite an important part in maintaining female ticks. Suggestion (b) at least should not be taken seriously until comprehensively investigated.

One author shows that an ‘appreciable’ tick population was maintained on a hill grazing by a reduced wild fauna in the absence of sheep.

Another author shows that the tick population of a grazing was considerably reduced by acaricidal treatment of sheep, together with almost complete extermination of a section of the wild fauna. Unfortunately, the two factors cannot be disentangled.

We would like to thank Mr Charles Elton, Director, Bureau of Animal Population, Oxford, and Dr J. MacLeod of the Cooper Technical Bureau, Berkhamsted, for criticism of the MS.; Mr F. Wallace for information on red deer stocking; and Dr V. B. Wigglesworth, F.R.S.,. Director, Agricultural Research Council Unit of Insect Physiology, Cambridge, within whose organization the work was done.

1. Eggs and larvae of Trichostrongylus retortaeformis were used.

2. The rate of hatching of eggs was shown to be mainly related to temperature. From November to March, when maximum temperatures were below 50° F., there was no hatching. When maximum temperatures of 50–55° F. occurred eggs hatched on or before the fifteenth day, but never during the first 8 days. Eggs hatched in 8 days or less when maximum temperatures of 60–80° F. occurred.

3. When the rate of evaporation in the air was high, eggs still hatched and reached the infective stage, the grass blades reducing the rate of loss of moisture from the faecal pellet. Laboratory experiments show that eggs may not develop to the infective stage if the faecal pellets are on a grassless portion of the pasture. This is most likely to occur when the rate of evaporation is high and the temperature low.

4. Hatching may be delayed by cold conditions, but some eggs remain viable for long periods and they hatch when the temperature rises. Eggs passed by the host in the autumn can survive a cold winter and hatch in the spring, but eggs passed during the coldest period die.

5. During periods when the maximum temperature never exceeded 55° F., little or no migration of larvae occurred. When temperatures rose above 55° F. the number of larvae migrating increased; but rise of temperature was associated with increase in the rate of evaporation. High rates of evaporation reduced the number of larvae migrating on the grass blades.

6. Some infective larvae died soon after exposure on grass plots, but a small number survived long periods. In cold weather some larvae were still alive after 20 weeks. A high death-rate occurred in warm weather. A large proportion of the larvae died during periods in which the rate of evaporation was high; in one of these periods 95% of the larvae were dead at the end of 4 weeks' exposure.

7. The number of larvae on grass blades of a pasture was shown to be dependent, at any time, upon the climate at that time, and upon past conditions which had influenced hatching and survival:

In March 1945 the writer had the opportunity of examining a young specimen of the South African lemur, Otolemur crassicaudatus garnetti, formerly known as Galago garnetti (Ogilby), sent into the Museum by Mr N. A. W. Macpherson from Cato Ridge near Pietermaritzburg, Natal. Fourteen Cheyletid mites were found in the fur on the back of the animal, some of them fairly active and none attached to the hairs of the body. In August 1946 a further number of mites belonging to the same family was taken from the fur of the slender mongoose, Myonax cauui punctulatus (Gray) captured at Mooi River. Finally, a number of larval Trombidiform mites were collected from the skin of a golden mole, Amblysomus hottentotus longiceps (Broom), donated by Mr R. S. Crass from Curry's Post near Pietermaritzburg.

Although three other Ixodes species were found, Ixodes ricinus L., when it occurs, is by far the most important tick parasite of wild and domestic animals on hill and moorland grazings in northern England. In the following, ‘tick’ or ‘ticks’ refer to I. ricinus.

The previous list of British mammal hosts, wild and domestic, to the tick (any stage) is largely confirmed, and increased approximately from twenty-three to twenty-nine species; and birds, similarly, from twenty-one to thirty-nine species. The preponderance of small mammals and birds among the twenty-four new-recorded host species confirms the impression that previous workers tended to confine their attentions to the larger animals. The host list is still incomplete, and the suggestion that the tick will parasitize any bird or mammal it may meet is strongly reinforced.

No host occurs below the reptile level among vertebrates; and among British reptiles, only the common lizard is a host—rarely. There appear to be no hosts among invertebrates.

All the farm and domestic mammals from horse down to cat are hosts to female ticks, but poultry have never been recorded—probably because they do not much frequent the tick-infested pastures.

Only the larger wild mammals and birds are hosts to female ticks. In northern England these include eight mammals and three birds. For Britain as a whole two other mammals are known, while a further four mammals and one bird are likely hosts.

With or without the inclusion of domestic animals, proportionately more mammal than bird species are hosts to female ticks. This is because there are more mammal than bird species large enough to be hosts.

All the recorded British hosts, except shrew and possibly mole, are hosts in some degree to nymphs, and all, without exception, are hosts to larvae.

A certain amount of self-deticking is practised by birds, and very probably by some of the smaller mammals. Birds never have ticks attached within beak-reach.

In the course of recent work on the pathogenicity of Trypanosoma vivax in bovines, cases have occurred at the Veterinary Laboratory, Entebbe, when it has been difficult to diagnose the species of trypanosome occurring in the blood. This difficulty arose because many of the trypanosomes were too small to be typical T. vivax and the possible occurrence of T. uniforme had to be considered, and also because many abnormal degenerate forms appeared at irregular intervals. A more detailed study of the trypanosomes present in the infection was therefore undertaken and, although in many aspects this work is still incomplete, the course of the infection in goats and sheep has been sufficiently interesting to merit this preliminary report.

1. The respiratory horn of Psychoda severini Tonn. subsp. parthenogenetica Tonn. is described. Within the tubular horn lies the felt chamber, which meets the horn wall at a number of thin circular regions, the pits, and communicates, through the annulated base of the horn, with the tracheal extension. This has a characteristic retiform thickening and is continuous, at the lower end, with the spiracular chamber, from which a trachea runs to the prothoracic spiracle of the imago.

2. At the upper end of the tracheal extension lies the closing mechanism consisting of a lever, and a muscle surrounded by a cuticular sheath. It is suggested that the mechanism functions by compressing the tracheal extension, and that the sheath serves to protect the muscle from the action of the moulting fluid.

3. The respiratory horns of fourteen of the British species of Psychoda are described, and it is shown that Ps. spreta Tonn., Ps. albipennis Zett. and Ps. trinodulosa Tonn. are like Ps. severini in possessing long lateral tubes in at least the basal half of the horn, whereas Ps. alternata Say, Ps. surcoufi Tonn., Ps. cinerea Banks, Ps. gemina Eaton, Ps. lobata Tonn., Ps. grisescens Tonn. and Ps. setigera Tonn. have only short lateral tubes. The two species Ps. phalaenoides L. subsp. elongata Tonn. and Ps. crassipenis Tonn. are alike in having a two-branched felt chamber, and Ps. brevicornis Tonn. has a flat triangular horn with a three-branched felt chamber and a cluster of air-containing tubes at each corner.

4. An account is given of the development of the respiratory horn of Ps. alternata Say. The horn arises as an outgrowth from the larval prothoracic imaginal disk, and the felt chamber forms by an invagination of its posterior wall. The tracheal extension arises as an invagination of the disk and subsequently acquires a connexion to the felt chamber.

5. The development is compared with that of Chaoborus plumicornis, and it is concluded that Weismann's theory of the origin of the horn from two distinct cell layers is not applicable to Psychoda.

6. The various terms that have been applied to the respiratory horn are discussed, and the conclusion is reached that though none of them is satisfactory, it is premature to devise a new scheme of nomenclature.

Grateful acknowledgements are due to Dr Ll. Lloyd for his help and advice in the course of this work. Some of the material was collected whilst the writer was in receipt of a grant from the Department of Scientific and Industrial Research, to whom acknowledgements are also due.

Four specimens of this parasite were collected from the gills of about two dozen Dussumieria acuta, a fish which is of market value in Madras. Of the four specimens, two were female and two were male; no two were found in the same fish. Both the males were 1·5 mm. long, while the two females measured 2·6 and 2·5 mm. respectively.

The egg of Ixodes ricinus L. is described, and the increase in size during development is noted. It is suggested that the increase is due to the absorption of water. The egg wall consists of exo- and endochorion with a thin vitelline membrane, which becomes thicker as development proceeds and assumes a laminated appearance. The secretion layer of Gené's organ is described, and appears to function as a cement for holding the eggs together in the cluster. Chemical tests show it to be of a waxy nature.

It is deduced from experimental evidence that the egg shell is not absolutely rigid, and the weight of evidence favours the view that the shape of the egg shell is maintained by the internal pressure of the egg contents, and the elasticity of the shell.

The development processes as seen in the living egg are described. Hatching from the egg shell is brought about by a muscular force acting on a limited area at the posterior pole of the egg.

The writer is indebted to Mr Robert David, of Longlands Farm, Pyle, Dr A. D. Lees, of the Agricultural Research Council, and Mr Simeon, of the Glamorgan War Agricultural Executive Committee, for supplies of material; to Mr T. W. Tyssul Jones, M.Sc., for his assistance in checking the measurements of the egg dimensions, and to Mr L. Cowley, M.Sc., Assistant Curator (Department of Zoology), National Museum of Wales, and Dr P. Tate, Molteno Institute of Parasitology, Cambridge, for reading the original script and for making many useful suggestions and modifications.

Joyeux & Baer, in 1935, recognized a new genus when they described Pseudoporrorchis houdemeri, a new species of Acanthocephala taken from the intestine of Centropus sinensis intermedius at Tonkin, Indo-China. They reviewed the literature and assigned four additional species to this genus as follows: Echinorhynchus rotundatus von Linstow, 1897; E. centropi Porta, 1910; E. bulbocaudatus Southwell & Macfie, 1925; and E. centropusi Tubangui, 1933. These same authors presented a tabular comparison of the five species, based upon all of the usual morphological details utilized in formulating specific descriptions. Morphologically the five species show close conformity in all essential features. In their host relations they are equally uniform in that each species utilizes some species of the avian genus Centropus as its definitive host. In the present paper a sixth species of this genus is described in which the same adherence to general morphological pattern is observed, although the definitive hosts are mammals instead of the customary bird hosts.

Observations have been made on the distribution of adult and pupal keds over the body of sheep and lambs, and the seasonal changes in density and distribution have been followed by a series of counts on the same sixteen sheep throughout a period of 13 months.

The method of assessing the adult population by counting the living keds was checked by killing and subsequently counting them, and is believed to give approximately correct results. Pupal estimations by the ‘live-count’ method gave results apparently 50 % below the actual values.

The ked population builds up rapidly during late winter and early spring to a maximum in April and early May. A decline begins in May, and by June the population has decreased very considerably. During summer the unshorn lambs show a continued decrease, which may be due in whole or part to loss by transference to the shorn sheep.

The greatest concentration during the peak infestation is on the chest, lower shoulder and lower rib wool. In winter and spring the population is more generally distributed, and may show a preference for the upper over the lower side wool. In summer the back is practically deserted and the upper sides only sparsely populated. The throat and chest region is a favoured site the year round, and there is some indication that the throat may be a breeding area.

Generally speaking, the adult and pupal populations are proportionately distributed. In late spring, however, puparia tend to be laid to a greater extent, relative to the adult population, in the lower than the upper surface fleece.

The significance of the seasonal population shifts is discussed, and a method of eradicating keds from a flock by summer dipping of the lambs is outlined.

An essentially synthetic medium has been developed for the cultivation of Entamoeba histolytica in association with organism t. It consists of buffered saline solution containing trace minerals, twelve amino acids, ten synthetic vitamins of the B complex, nucleic acid, cholesterol and rice starch. Cultures have been carried continuously in this medium for a period of eleven months.

We are greatly indebted for materials used in this study to the following: Drs M. S. Dunn, J. J. Eiler, D. M. Greenberg, L. D. Greenberg, E. E. Howe, H. D. Lightbody, H. S. Loring, H. Molitor, E. D. Stewart and E. L. R. Stokstad.

The authors wish to acknowledge the valuable advice and material aid provided by Drs Gladys Emerson and Gilberto G. Villela during the initial phase of this study.

In recent papers I have given, in relatively compact form, lists of the genera and species of metastrongylid lungworms; these publications are in turn summarized in a paper which follows (Dougherty, 1948). However, the trichostrongylid lungworms, constituting the subfamily Skrjabingylinae Skriabin, 1933, have not been completely treated, although in a recent work (Dougherty, 1945), in which certain lungworms were formally transferred from the Metastrongylidae to the Trichostrongylidae, the Skrjabingylin genera were listed without critical appraisal, and in the same paper the genus Crenosoma Molin, 1861, was reviewed in detail; subsequently the genus Dictyocaulus Railliet & Henry, 1907, has also been reviewed (by Dougherty, 1946).

A new species of the giant phyllobothriid genus Dinobothrium (D. keilini n.sp.) is described from the blue shark (Carcharinus glaucus); it is compared with D. planum Linton, found for the first time from British waters, in the basking shark (Cetorhinus maximus), and the structure of both is discussed in relation to that of the genotype, D. septaria van Beneden. A fourth species, D. paciferum n.sp., also from the basking shark, is described, and though only a tenth the size of the other species, it shares most of their diagnostic scolex characters. It has eight true suckers above the four pendent bothria: in D. planum there are four true suckers and four pseudo-suckers, while in D. keilini there are only four true suckers, and D. septaria is said to have four pseudo-suckers alone. The nomenclature of the older species is revised, and the genus redefined.

Attention is directed to the adaptations in these large cestodes which facilitate interchange with the substratum: the development of lateral furrows through which the main excretory canals open to the exterior. There is also a ventral furrow, which in the nascent segments is an open cleft: this accommodates the growing uterus and permits a protracted gravid phase of the proglottides in situ. The effect is of five longitudinal hinges, which allow of considerable lateral expansion of the thick-walled strobilus. The smaller D. paciferum lacks these modifications, and the cylindrical segments are apparently detached in the gravid state. An explanation is offered for the conflicting accounts of the lateral extent of the vitellaria in this genus: there is a lateral contraction of the ventral vitelline reticulum as the ovarian phase waxes. In D. paciferum the vitellaria completely encircle the proglottis at the inception of the ovarian phase.

Notes are given on the selachiàn hosts examined, their food and the other parasites present. The relationships of Dinobothrium to other phyllobothriid genera and to Tetrabothrius are discussed.

In one electric ray, Torpedo nobiliana, a single immature strobilus of another kind of phyllobothriid was found; it is probably a new species of Monorygma, though it has slight resemblances to Calyptrobothrium—a genus characteristic of electric rays. The boat-shaped bothria are held at an angle from the scolex by contractile buttress-like wings, and at their proximal end there is a relatively large and complex sucker. Affinities with related genera are discussed and the nomenclature of Monorygma angusta (Linton) is emended.

1. History of the classification of the family Metastrongylidae is briefly reviewed.

2. The probable origin of the family is discussed. It is believed that the metastrongylids arose, in common with the family Strongylidae, from a primitive group of eustomatous, cloacinin-like, gastro-intestinal strongylines that were symbiotic with an ancestral mammalian group, possibly the pantotheres. One group of these symbiotes established itself in the mammalian respiratory tract and originated the metastrongylid line.

3. The family Trichostrongylidae is regarded as of common origin with the family Ancylostomatidae from eustomatous ancestors. Thus meiostomy in the metastrongylids and trichostrongylids is convergent.

4. The Metastrongylidae consist of three main lines, each characteristic of a placentate order: the Filaroidinae in the Carnivora, the Pseudaliinae in the Cetacea, and the Protostrongylinae in the Artiodactyla. These lines probably have evolved from a common ancestor, symbiotic with a host at the base of the carnivore-cetacean-ariodactyl radiation. Certain forms have become secondarily adapted to symbiosis with members of other placentate orders.

5. Morphological and biological evidence is given for each of the foregoing phylogenetic conclusions.

6. Metastrongylus Molin, 1861, is regarded as a relict genus. With it, in a subfamily Metastrongy-linae, is placed the genus Heterostrongylus Travassos, 1925.

7. Heterostrongylus is represented by a single known species, H. heterostrongylus Travassos, 1925, from an opossum (order Marsupialia). Morphologically it is primitive with cloacinin-like cephalic features. In view of the phylogenetic status of its host it may well represent an ancestral type that has evolved along with the Marsupialia from a common ancestry with the other metastrongylids, probably in the panthotheres. As yet unknown lungworms of marsupials may shed light on this interesting point.

8. Diagnoses are given for the family Metastrongylidae and its subfamilies; the twenty-two component genera are listed under the latter. New synonymies are made: Neometastrongylus Kreis, 1944, a synonym of Neostrongylus Gebauer, 1932; Neometastrongylus buechii Kreis, 1944, of Neostrongylus linearis (Marotel, 1913) Gebauer, 1932; and Otophocaenurus Skriabin, 1942, of Pharurus Leuckart, 1848. Otophocaenurus oserskoi Skriabin, 1942, becomes Pharurus oserskaiaae (Skriabin, 1942, n.emend.) n.comb.; Metathelazia massino becomes M. massinoi (Davtian in Skriabin, 1933, n.emend.) Dougherty, 1943.

Trypanosoma cruzi is easily cultivated in tissue cultures of chick embryos, but it was not possible to infect chicks with trypanosomes cultivated for more than 2 years in chicken cells.

The trypanosome cycle takes place in one cell unit.

The number of trypanosomes formed in one cycle depends on the volume of the host cell.

The transformation of the leishmania form into the flagellate form begins when the cell is full of parasites, and occurs in 12–24 hr.

The intracellular trypanosome, immediately after the crithidia form, is broad and short, the thin form probably being a later phase of the evolution of the parasite.

Division of the adult trypanosome, or mating between the thin and broad forms, was never seen.

At the beginning of the infection the cells with-stand the parasites and continue to proliferate, but finally they are destroyed.

It is a common observation that in individual Ixodes ricinus L. ticks, size variations occur; such variation is reflected in the records of early workers (Wheler, 1899; Neumann, 1899: quoted by Nuttall, Warburton, Cooper & Robinson, 1911). The present paper attempts to examine the true specific importance of size variation by basing the study on measurements of the relatively inelastic scuta after the principle of using head capsule measurements for insectan larval instars.