Small trematodes were observed by Dr G. S. Carter and Mr L. C. Beadle in the pericardiac cavities of Lepidosiren paradoxa caught in the swamp at Makthlawaiya in the Gran Chaco, during the months January to June 1927. The infected Lepidosiren varied in length from 20 to 34 ins., and constituted almost one-half of all the fish collected during that period. Dr Carter tells me that the infected fish appeared to be in perfect condition. Specimens from fifteen fish were preserved, and have been examined.

During trawling expeditions off the coast of Galway in 1926–1928 I examined 100 specimens of Solea vulgaris Quensel, of varying sizes, and found about 60 per cent. infected with the parasite herein described. Usually two to five parasites were found attached to an infected fish, but up to eight were discovered on a single host.

Watson-Kamm (1916, 1922) has given complete lists of cephaline gregarine parasites from different classes of hosts, discovered up to 1920. She concluded that “except in rare instances a species is confined to a single host or to nearly related hosts, not being found in insects as far removed from each other as the Coleoptera and the Orthoptera.” She belives there is an interesting parallelism between the complexity of the parasite and the group of hosts in which they are found. The simpler forms occurring in the Crustacea and Diplopodia, and the higher and more complex forms being found in various orders of Insecta. Many instances could be mentioned in which genera are found exclusively in a single order of insects.

While working on parasites of fish for the New York State Conservation Department during the summer of 1928 it was possible to secure experimental evidence on the life-cycle of Proteocephalus pinguis La Rue 1911. The adult parasite lives in the digestive tract of Esox lucius Linnaeus and E. reticulatus Le Sueur where it ranges in length between 50 and 90 mm. Since La Rue (1914) gives a complete description of the adult it is not necessary to go further into the morphology of this form. Adult tapeworms for the experiments were taken from E. lucius from Lake Erie and Ellicott Creek, near Buffalo, New York, and from E. reticulatus from Barrett and China Ponds near Carmel, New York.

1. Previous work by the writer drew attention to the fact that the pH index of natural waters was in some manner correlated with the presence or absence of particular mosquito larvae.

2. The observation led other investigators to study this hypothesis, and a short summary of their published records is given.

3. The actual significance of the pH index was, however, obscure, and the present work has been undertaken to attempt to demonstrate the actual significance of the pH in mosquito breeding-places.

4. By gradually eliminating first one and then another of the interacting factors, the writer has been able to demonstrate (a) that if the pH of the normal environment is changed the development of the larvae is adversely affected; (b) that under bacteriologically sterile conditions the foregoing statement is no longer true; and (c) that consequently the acid or alkaline reaction of the medium, within ordinary limits, has no direct effect upon the development of the larvae.

5. Nevertheless, it is shown that the influence of the pH. is of unquestionable importance and that its significance lies in the fact that, under natural conditions, it indicates the favourable or unfavourable association of chemical and biological factors in the breeding-places upon which the successful or unsuccessful development of the larvae depends.

6. It may therefore be stated that although the pH index is not an infallible guide, it does in the majority of instances provide a reliable index as to whether the necessary combination of chemical and biological factors in any given water are such that they will permit the development of the larvae of particular species. Some species find their optimum conditions for development in waters which are acid, others in waters which are alkaline, and it can be shown that to alter the pH of such waters is often to bring about a complete change in the biological group associations, which frequently means the acquired abnormal dominance of factors unfavourable to a particular species of larvae. Clearly, the system is to some extent elastic, and in rare instances what are in general acidophile larvae may be found in waters showing alkalinity.

7. The chief conclusion is, however, that in most instances in various localities the larvae of certain species do actually show a restriction to waters exhibiting a pH index within a definite short range, and that the pH index is consequently often a reliable index also as to whether the chemical and biological group associations will favour or preclude the successful development of such larvae.

8. A new technique is described for the production of a high percentage of successful cultures of Aëdes argenteus larvae and pupae under bacteriologically sterile conditions.

9. The phase of “suspended development” has been investigated and is found to have its probable explanation in the temporary or complete disappearance of micro-organisms on which the conversion of the organic materials of the environment, to a suitable larval diet, depends.

In the course of a Mosquito Survey carried out in the neighbourhood of Birmingham on July 31 and August 1, 1928, a large number of female mosquitoes of the two species Aëdes (Aëdes) cinereus and Aëdes (Ochlerotatus) annulipes were collected and subsequently examined.

Anoplura without eyes; with four segmented antennae not dimorphic in the sexes; 1 well developed sensorium on 4th antennal joint postero-basally; head considerably contracted posteriorly. Segments I–III closely united, more distinctly separated from the rest of the abdomen than the succeeding segments are inter se. 2nd sternite divided. 3rd cap-shaped.

While investigating the species of Corallobothrium (Essex, 1928) I examined the intestinal parasites of 180 channel catfish (Ictalurus punctatus) taken in Rock River (Illinois). Only six of these fish harboured tapeworms that could not be assigned to the genus Corallobothrium. From the six fish, besides the species of Corallobothrium, I found fifteen adult Cestodes belonging to the genus Crepidobothrium. A study of these parasites has shown that they constitute a new species for which I propose the name Crepidobothrium fragile, because of the ease with which the strobila is broken. The members of this genus have been reported previously only from amphibians and reptiles. This is, so far as I am aware, the first recorded occurrence of a species of Crepidobothrium from a fish host. Nybelin (1917) has shown that the genus Ophiotaenia (La Rue, 1911) is synonymous with Crepidobothrium. It has been pointed out by Woodland (1925, 1925a) that the characters used by La Rue (1914) as the basis for the separation of the genera of Proteocephalids have been unreliable because of their inconstancy. He has proposed that all the genera of the family Proteocephalidae be placed in the genus Proteocephalus. Meggitt (1927) has indicated that this procedure is too sweeping and if followed would make “a most heterogeneous assemblage of some 100 species.” Therefore, he has placed all these species under four genera, namely, Corallobothrium, Crepidobothrium, Gangesia and Ichthyotaenia (= Proteocephalus), all of which have been well established for a number of years, and greater confusion of the literature may be avoided if they are retained until some worker, in the light of more complete knowledge, again makes a revision of the entire family. Since there yet remains some doubt as to the characters that will ultimately prove trustworthy in the classification of the Proteocephalids, descriptions of new species should be as complete as possible. Although there is much variability in the measurements of a given species of Cestode, yet the fact should not be overlooked that the range of size of the organism and its parts is of considerable aid in classification. It is admitted that there is great variability in size in a given species of Cestode, but if the extremes are known the size becomes of significant value.

On many occasions during the years 1921 and 1922 I devoted my leisure to collecting Cestode and other Helminth parasites from wild birds in the United and Central Provinces of India. A large proportion of the material collected consists of species already known but the remainder contains some new and interesting forms, and three of these I am describing in the present paper.

It has been shown in an earlier paper that if the eggs of parasites are not deposited in unparasitised hosts alone, but distributed according to the laws of chance among unparasitised hosts and hosts already attacked by individuals of the same species, and if all the parasites develop successfully, no matter how many enter a single host, then the effect upon the time required for the extermination of the host, as compared to that which is required if only unparasitised hosts are chosen, is relatively slight.

The hypothesis examined in this paper is that when several parasites enter a single host, one, and only one, will develop successfully. It is shown that in such a case, provided the reproductive rate is decidedly greater than that of the host (e.g. 1·5 times as great), the effect on the time required for the extermination of the host by the parasite will be very little if at all greater than when superparasitism causes merely a loss in efficiency, as in the hypothesis previously examined. When the reproductive rate of the host is practically or actually equal to that of the parasite, the process of control will be seriously retarded, the delay being very much greater than in the preceding hypothesis. Control will, however, occur, even in this case.

Superparasitism of the type here examined will therefore not necessarily produce any marked retardation of the process of control in cases where control within reasonable time would otherwise be probable.

A large number of fresh-water Invertebrates has been examined and the parasites obtained from them include examples of the commoner groups to be met with in any area surveyed. Six larval Trematodes have been described in detail, and by means of direct animal experiment two of them have been definitely related to known adults. Of these two one is the larva of Notocotylus seineti Fuhr., and is doubtfully Cercaria monostomi v. Linst., while the other is the larva of Echinoparyphium recurvatum v. Linst., and is described here in detail for the first time. The four xiphidiocercariae described are new. Data relating to the activity, duration of free life, and process of encystment of cercariae within the bodies of secondary intermediate hosts is also given.

Effect of the parasite on the host. The disruption of the tissues brought about by the presence of sporocysts or rediae in the liver of a mollusc injures the host, and in many cases brings about its death. The gonads also are often attacked and completely destroyed. This latter feature of parasitic castration has been observed by Giard (1888) among certain species of Limnaea, Planorbis and Paludina attacked by sporocysts. Brown (1926) states that the gonads are rarely infected. As regards the encysted stages of cercariae these appear to do very little harm to their hosts even when present in large numbers. These observations are in agreement with those of Lebour (1912) for the sporocyst, rediae, and encysted stages of marine Trematodes.

Double infection. I have found no instance of a double infection among the species described. In the literature, several records show the parasitism of two or more species of cercariae, within one and the same host. The occurrence of two species is most commonly met with, and as a rule one is in predominance. Sewell (1922) states that double infection is not common in India. Faust (1917), on the other hand, has found as many as four trematode species within the same host individual (Planorbis trivolis). Hesse (1923) states that “every large Limnaea peregra examined was heavily infected with sporocysts of either of the two species, but it was rare to find both together.” Brown (1926) in the neighbourhood of Birmingham has found three examples of associated xiphidiocercariae and furcocercariae, one example of xiphidiocercariae and echinostome cercariae, and two examples of echinostome cercaria, all from Limnaea stagnalis L.

A cotylocercous cercaria occurring in the marine snail, Astraea americana, at Tortugas, Florida, was found to encyst in small fish as second intermediate hosts.

Fish experimentally infested with the cysts were fed to the gray snapper, Neomaenis griseus, and adult worms developed in the intestine and pyloric caeca which were identified as Hamacreadium mutabile Linton, 1910, a member of the sub-family Allocreadiinae.

A general relationship of the cotylocercous cercariae to the family Allocreadiidae is discussed.