The material here described was mostly obtained as a result of a period of study and travel in East Africa in 1939. Two of the species were reared from Coccidae of the genus Aspidoproctus at Amani, Tanganyika Territory, and their life, history is the subject of an accompanying paper. I am greatly indebted to Dr F. W. Edwards, F.R.S., for allowing me to describe the remarkable species collected by him on Ruwenzori, Uganda, in 1935. I am also most grateful to Dr R. H. Le Pelley of the Scott Agricultural Laboratories, Nairobi, and Dr E. A. Lewis of the Veterinary Research Laboratory, Kabete, Nairobi, for other valuable new material. In addition, The Imperial Institute of Entomology has kindly allowed me to examine and describe material from Uganda in their possession which had been erroneously identified as Cryptochaetum iceryae (Will.). Type specimens of all species will be deposited in the British Museum.

Tropical and certain parts of subtropical Africa constitute the home of the genus Aspidoproctus (Coccidae, Monophlebini). The genus is remarkable in several ways, but chiefly because of the very large size attained by some of the species. A. maximus and A. giganteus are almost certainly the largest scale insects in the world, the female being well over 1 in. long and as much as ¾ in. thick. Owing to the relatively degenerate structure of scale insects in general, and in particular because of the poor development of the circulatory and tracheal systems, the biology of scale-inhabiting parasites is always of interest. This is particularly the case in relation to problems of respiration, and many scale parasites are already known (Thorpe, 1931, 1934, 1936) which exhibit very striking respiratory adaptations. Previous to the present paper no parasites had been recorded from the genus Aspidoproctus, yet it appeared extremely improbable on general grounds that these insects were immune from the attacks of the usual dipterous and hymenopterous parasitoids. Accordingly, when opportunity came to visit East Africa, attention was directed particularly to this problem; for it was felt that with insects of such large size and having such a thick dorsal cuticle, the problems to be overcome by the internal parasite would be intensified tenfold, and that any species found would be likely to exhibit structural and physiological adaptations of unusual interest. That this is indeed the case the present paper will show.

We received from Dr W. H. Thorpe a remarkable Eupelmid bred from the large Coccid, Aspidoproctus maximus Newstead, in East Africa. As Dr Thorpe has been able to make some interesting observations on the life history of this parasite, I have been asked to study it specially. It differs from all other known species of Eupelmus from Africa, and I am giving here a description of that species.

The present work, fills in some of the gaps in the morphological descriptions of Hemimerus, as given by Hansen (1894) and Jordan (1909), and deals with the details of the anatomical modifications associated with the semiparasitic mode of life.

It seems that this semiparasitic mode of life is of mutual assistance or “symbiosis”.

The modifications are seen in the mouthparts (especially the ligula and the superlingua), pleural sclerites and the thoracic limbs.

An account is given of some Microsporidia found in certain fishes and insects in eastern Canada, among which are new species of Nosema, Perezia and Gurleya.

Nosema pimephales n.sp. produces large cysts or tumours in the abdomen of Pimephales promelas, one out of a large number from Lake Guindon, Province of Quebec, being infected.

Nosema branchiale Nemeczek has been observed from a cod, Gadus callarias. The organism is shown to be a Nosema, though the incomplete original description has caused doubts as to whether some other genus was involved. Further details are now given.

Nosema apis Zander and N. bombi Fantham & Porter have been found in Canada in hive-bees and humble-bees respectively, the latter being recorded from a new host, Bombus vagans.

Glugea hertwigi n.var. canadensis is described from Osmerus mordax from Lake Edward.

Perezia aeschnae n.sp. has been found in nymphs of the large dragonfly, Aeschna grandis, collected near Montreal and is described and illustrated.

Perezia legeri Paillot has been observed in larvae of Pieris brassicae.

These appear to be the first records of Perezia from insects in North America, and the zoogeographical distribution of the genus is extended to the Odonata.

Gurleya aeschnae n.sp, is described from a nymph of Aeschna grandis. It is the first species of Gurleya to be described from the Odonata and the first record of the genus from the North American continent.

Thelohania corethrae Schuberg & Rodriguez is described from the larvae of Chaoborus flavicans. Measurements of the parasite, which were lacking in the original description, are now supplied.

Thelohania bracteata from larvae of Simulium bracteatum and larvae and one adult S. venustum and Thelohania fibrata from larvae of Simulium venustum are recorded from places in the Province of Quebec. The need of reinvestigation of the species of Thelohania from various Simulium and the possibility of there being but one species, Thelohania varians Debaisieux, are indicated.

Thelohania legeri Hesse is recorded as a parasite of larvae of Anopheles punctipennis in Quebec Province and of A. gambiae in Zululand. It is probably the most widely distributed species of Thelohania, occurring in Anophelines in Europe, Asia, Africa and North America.

Some general remarks regarding zoogeographical distribution, habitat, host-specificity and possible origin of species and varieties in connexion with Gurleya, Perezia and Thelohania are presented.

While making a survey of the parasites of littoral fishes at Cullercoats, Northumberland, parasites from Mola mola and Raniceps raninus came into my possession. These fishes are rarely found in British waters and so far no parasites have been recorded from R. raninus in British waters.

In a paper at present in the Press, we have endeavoured to show that where moderate or high infestations of men with Pediculus humanus corporis are present, the maintenance of these, and the level at which they tend to remain, are not dependent on the environment of the infested subject. The degree of infestation is a reflexion of the subject's recent standards of personal hygiene, and his habits at a given moment mould the structure of his infestation in the future.

1. The osmotic behaviour of three parasites in normal and experimental media has been studied with a view to understanding the relationship with their hosts.

2. Angusticaecum sp., a nematode frpm the intestine of the tortoise, is hypertonic in media of very low concentrations (1·1–1·3 % NaCl in tap water), but becomes isotonic in sea water and slightly hypertonic in 50 % sea water. Ligaturing experiments show that its cuticle is permeable to water and probably to salts.

3. Lernaeocera branchialis, a blood-feeding copepod from Gadus spp., is hypotonic to the surrounding sea water so long as it remains attached to its host, its blood showing an osmotic pressure equivalent to 2·O–2·8 % NaCl. Isotonicity with the medium is established when the parasite is excised and kept alive. Hypotonicity of Lernaeocera is probably caused by the low osmotic pressure of the blood of its host (1·443 % NaCl in Gadus pollachius), to which it is permanently attached.

4. Bopyrus squillarum, a blood-sucking isopod from Leander serratus, is isotonic or slightly hypotonic to sea water, the tendency towards hypotonicity being probably the result of the hypotonic nature of the blood of the host.

5. The osmotic properties of Lerpaeocera and Bopyrus would suggest their ability to survive in dilute sea water, a fact which is supported by their occurrence on hosts living in inshore or estuarine habitats.

1. In three previous papers (1936, 1938b, 1940a) the author has discussed the distribution of head-lice among their human hosts, his material being nearly 3000 complete crops of hair. The present paper deals with the strictly entomological side of the inquiry, that is to say, with the study of the populations of head-lice themselves. The total amount of material is the lice from 858 infestations from six places; from each of four places there were less than 100 infestations.

2. In about two-thirds of the infestations there were ten lice or less, the proportion of low infestations varying considerably from place to place (Table 1). Infestations over 100 never formed more than 10% of all the infestations in a place.

3. In a single head the proportion of the sexes is often far from equal; indeed, in light infestations it is common to find that all the adults are of one sex. Taking all the heads from one place, the total number of males and females differs significantly from equality, an excess of males occurring in one place, of females in another (Table 2). In all heads from one place the coefficient of correlation between the number of males and females is high, about 0·8–0·9. As the density of the louse population, does not generally affect the sex ratio, the correlation is approximately linear. But when the density is unusually high, as it is in some heads from Colombo, the proportion of males rises progressively. This is the only case known, in spite of much searching, in which sex ratio of the louse is affected by an environmental factor.

4. In the matter of the number of larvae per female, there are great individual differences between heads, though the coefficient of correlation, worked on all the heads from one place is as high as 0·7 or 0·9. Taking all the heads from one place, the mean number of larvae per female ranges between 5·4 and 10·9; many of the differences between places are significant. I have failed to find any explanation of these differences, and they do not seem to be affected by any environmental factor. The fact that the larvae are always more numerous than the females, indicates that there is a high mortality during the course of larval life; the author has failed to make a more precise estimate of the proportion which die.

5. A small part of the material was specially examined, and every larva referred to its instar. In this sample of 502 larvae it was found that the death-rate was higher in the third instar than in the other two, a state of affairs the reverse of what occurs in body-lice reared in boxes.

The hatching of the eggs of Pediculus humanus corporis De Geer is influenced by temperature.

High temperatures accelerate and low temperatures delay development.

The lowest constant temperature at which eggs will hatch is 24° and the highest 37°.

At 24° eggs begin to hatch on the seventeenth day and continue hatching until the twenty-first. At 37° eggs hatch on the sixth and seventh days. The temperature at which eggs hatch in the shortest time is 35° and the time 5 days. At these extremes many eggs are killed so that the percentages of successful hatches are very low. Eggs are killed by 2 days' exposure to 39°.

Temperatures at which the maximum number of eggs hatch he between 29 and 32°. In this range of “favourable” temperatures, up to 97% of successful hatches may be recorded. The incubation period is from 7 to 11 days. This is a convenient range of temperatures for laboratory purposes and gives largest numbers in a reasonably short time.

Newly deposited eggs will not hatch if kept for 14 days at 23° or for shorter periods at lower temperatures, until at 8° exposure for 7 days is sufficient to ensure that all eggs are dead.

If partially developed eggs are exposed to temperatures of 15° or lower, development ceases. If they are restored to a favourable temperature within 7 days, development is resumed and some of the eggs will hatch.

Older eggs which have almost reached hatching point at a “favourable” temperature hatch if transferred to temperatures as low as 18°. They do not hatch at 15° or lower if kept at such temperatures for at least 9 days.