(A) Life History.

(1) Simulium larvae are found in streams where the current is very fast. They are sedentary in habit and fix themselves to some support by means of their posterior sucker and sticky salivary secretion.

(2) Progression is achieved by looping movements which have been described in detail.

(3) Larvae feed on all kinds of fresh water animalcules, and algae.

(4) Two species were reared from eggs to the adult flies for the first time in the laboratory. Abundance of food and aeration of water are two very important factors governing the rearing of these larvae.

(5) There are six larval stages, each stage lasting 4–7 days. The gradual changes in the successive stages are described in S. erythrocephalum and S. aureum.

(6) The sixth-stage larva, having woven its cocoon, changes into a pupa, the whole process, weaving of cocoon and pupation (described in detail), takes 75–90 minutes. Pupal life lasts 5–15 days, depending on temperature.

(7) The eggs are sub-triangular in form and are laid in large patches on aquatic plants below the surface of water.

(8) The first-stage larva is characterised by the presence of an egg-burster situated dorsally upon the head.

(B) Morphology.

(9) The larvae are eucephalous, with eleven faintly marked body-segments, three thoracic and eight abdominal, the eighth abdominal being apparently divided into two parts, the posterior carrying the anus and posterior sucker. There is a median uniramous thoracic proleg which like the posterior sucker is provided with a number of cuticular hooks.

(10) The head has a number of markings which are of great taxonomic importance.

(11) The head-appendages are: A pair of jointed antennae, a rounded labrum, a pair of lateral fan-shaped appendages (the premandibular organs), a pair of mandibles, a pair of maxillae each with a single-jointed palp, a hypopharynx, and a labium. These appendages have been described in detail in this paper for the first time.

(12) The alimentary canal, malpighian tubules, salivary glands, muscular system and gonads are dealt with in detail.

(13) The oesophageal valve has no blood sinus as has been erroneously described by previous writers.

(14) A pair of dorsal glands are present above the pharynx. Their walls consist of large uninuclear cells. Dorsal glands have so far been found only in Sciara among Dipterous larvae.

(15) There is a well-developed central as well as visceral nervous system. The bilobed brain lies in the head and a chain of eleven ganglia in the body. Both the supra-intestinal and the infra-intestinal visceral systems are fully worked out for the first time.

(16) There is a well-developed tracheal system with ten closed spiracles, one prothoracic, one metathoracic and eight abdominal.

(17) The flattened dorsal vessel stretches from the seventh abdominal segment to the head where it ends just behind the brain. It is dilated in the seventh segment to form the heart which is provided with two pairs of ostia.

(18) Nephrocytes or excretory cells (pericardial, and peri-oesophageal) are described for the first time and compared to similar structures in other Dipterous larvae.

(19) A detailed description of the early stages of all the known (seventeen)1 British species is given, with remarks about eleven of them, as they occur in Sweden, Norway and France.

(20) The characters used for determining the species are as follows: Larva. Head markings; antennae; mandibles; submentum; anal gills; ventral papillae; and posterior sucker. Pupa. Chaetotaxy, Respiratory filaments, and Cocoon.

When La Rue (1914 a) published his exhaustive monograph on the Proteocephalidae, all the then-known species of this family were, with one exception, shown to be very much alike. To substantiate this statement it will suffice to mention that all the six genera, into which La Rue grouped the species, were chiefly based upon trivial characters of the scolex and the distribution of the testes. The one exception referred to was the species which he re-named Monticellia coryphicephala (Monticelli), and this species differed from all the others in the remarkable and relatively deep-seated character of its principal genital organs being situated in the cortical region of the parenchyma instead of in the medullary. This one exception was promptly transferred by La Rue to a distinct new family, the Monticellidae, and the consequence was that he was still left dependent upon the aforesaid trivial characters as bases for his genera in the original family. Since 1914 however we have come to know of some other Proteocephalids exhibiting similar deep-seated differences of structure, and we are therefore in a position to re-consider the classification of the Proteocephalidae on broader lines, including Monticellia coryphicephala in that family. The general scheme of this re-classification I have already outlined in a paper (Woodland, 1925 a) which will be published either before or shortly after the present communication, and it is my purpose, in this latter, to justify the suggestions there referred to by discussing the subject in some detail. Before attempting this, however, I shall describe the structure of three new Proteocephalids, two from India (in a frog and a Varanid lizard) and one from the Sudan (in a Siluroid fish).

This worm was obtained from the intestine of Sarcogrammus indicus Stoliczka at Nagpur, C.P., India. It was flattened out between two glass slides, fixed in Mann's fluid and stained with Delafield's haematoxylin. The measurements of the worm given in the following description relate to the flattened specimen.

N. A. Cholodkovsky was born on the 4th of March 1858 at Irkutsk, Siberia, where his father was a physician. He attended school in St Petersburg (now Leningrad) and at the age of 17 entered the Academy of Medicine. After completing his medical education, having no inclination for practice, he joined the University and in 1885 obtained the lectureship of Zoology in the Institute of Forestry.

In the course of the examination of the contents of the paunch and rumen of 70 Ruminants a Ciliate of an interesting type has been met with on eight occasions. It is surprising that a new form should be found in this situation as a number of workers seem to have devoted no little time to researches on the fauna of the ruminant stomach. One cannot think that this animal is to be found only in England, and we are driven to the conclusion that it must have been overlooked up to the present. As the organism is relatively small for a Ciliate and of a rather transparent appearance this is understandable, especially because it is rarely abundantly present. Although it has been found eight times, yet in a coverslip preparation where there will be several specimens of the other Ciliates in every field of the microscope, there may not be more than one or two specimens of this new form.

Through the kindness of my friend Mr Clifford Dobell, F.R.S., I have come into the possession of a quantity of preserved stomach-content from the Mouse Deer of Ceylon (Tragulus meminna Milne-Edwards). As there are no descriptions, so far as I can find, of the Ciliates from Asiatic Ruminants, it seems worth while to publish a brief note on the organisms found in this material.

The genera Citellinema and Warrenius were established by Hall in 1916 with regard to specimens collected from alcoholic host material supplied by Mr E. R. Warren. The genus Citellinema was founded upon a single male specimen from Citellus elegans, named by Hall Citellinema bifurcatum, in reference to the bifurcated spicules. The genus Warrenius was based upon two males, one headless, from Eutamias quadrivittatus, to which Hall gave the name Warrenius quadrivittatus.

Owing to the courtesy of Dr G. M. Vevers I have had the opportunity of examining a marine Ichthyobdellid leech, taken by Dr F. A. Phillipps from the cloaca of a shark, 7 feet long, caught between the islands of Aore and Santu, New Hebrides. The leech resembles Pontobdella superficially in being covered by warty tubercles. It possesses, however, certain peculiarities described below which justify its recognition not only as a new species but also as a representative of a new genus.

Bertiella satyri, normally apparently a parasite of apes, has hitherto been recorded from the orang-utan, Simia satyri, in Borneo, and once from a child in Mauritius.

There has been much difference of opinion as to the specificity of Strongyloides in different hosts, therefore an opportunity has been made use of to compare representatives of this genus, in various stages of their life histories, from monkeys, cats and man, and to compare these with the published characteristics of other forms.

B. anthracis, S. faecalis and B. subtilis were found to survive, the first two indefinitely, in the alimentary canal of Argas persicus, and to be passed in its faeces. The stomach contents, in vitro, were bactericidal to B. anthracis, but in some of the tests a few individuals survived, and these may represent more resistant organisms, or spores, to which the infection of the tick by the relatively massive doses used in the feeding experiments was due. In smears of the stomach contents and faeces of the tick, B. anthracis appeared as a short thick bacillus in chains of about three to eight individuals provided with a very well-developed capsule. This capsule, not present in the agar cultures used for the bactericidal tests, may have afforded the bacillus protection within the tick. If this be true, then a very small dose of the capsulated bacilli from the blood of an infected animal might succeed in infecting the tick. A culture of B. anthracis recovered after one hundred days in the tick was found to be fully virulent and pathogenic.

B. subtilis seemed to behave like B. anthracis in the tick, but the investigation of this micro-organism was much less complete than that of B. anthracis. There is an apparent discrepancy between the results of the feeding experiments and the inhibitory tests in vitro. This might be explained by assuming that the two ticks which harboured the bacillus to the end were deficient in the inhibitory principle, which, as shown above, is not equally active in all ticks, or by suggesting, on analogy to the bacteriophage, that the inhibitory element was completely absorbed by the large bacterial dose used in feeding, leaving an excess of bacilli to establish the infection. This might also be put forward as an alternative explanation in the case of B. anthracis.

All the experiments with Streptococcus faecalis were consistent, and showed it to be an organism wholly resistant to the bactericidal and inhibitory elements in the tick's stomach. B. mycoides neither survived long in the tick nor appeared in its faeces. Only four ticks however lived, and of these only two were available for examination; a number perhaps too small to justify any definite conclusion being drawn from purely negative results. Why this bacillus should have behaved differently to the other sporing bacilli, B. anthracis and B. subtilis, is not apparent. It was not more susceptible to the lytic action of stomach contents than was B. anthracis, and, unlike B. subtilis, it was wholly resistant to the inhibitory principle.

Tests with B. pestis and B. melitensis were inconclusive, as both of these micro-organisms died out soon in the inactivated horse serum used in feeding; B. pestis in two weeks and B. melitensis in about three weeks. In the case of B. melitensis the organism apparently survived as long in the tick as it did in the serum control. In order to obtain more conclusive results with these two organisms, it is necessary to find a medium which, while providing a suitable food for the tick, will not prove inimical to the life of the bacillus. It is noteworthy, however, that the growth of these organisms was not inhibited, and B. melitensis was not destroyed, in vitro by ticks' stomach contents.

B. typhosus presented a curious problem in that, while it survived in the stomach for at least twenty-two days, it was never recovered from the faeces; this applies also to the case of B. melitensis. Whether or not this is due to some factor existing in the rectum or malpighian secretion, has not been shown. The cause of the eventual disappearance of B. typhosus from the tick is obscure. It may be that it is killed off by the products of its own life activities in a medium particularly favourable to its growth. No lysin or inhibitory principle affecting B. typhosus was found in the tick.

Staphylococcus aureus furnished very conclusive results. It died out quickly after ingestion by the tick, and the evidence of the feeding experiments was fully supported by the results of the tests in vitro which showed the stomach contents to be powerfully bactericidal and inhibitory to the coccus.

The source and nature of the lytic and inhibitory principles require further investigation which will be made the subject of a later communication by one of us (J.T.D.). For the present, the results of the control cultures on horse serum make it clear that this medium is not the source. Other tests carried out with the inactivated blood of the fowls used for the normal feeding of the ticks gave no appreciable evidence of bactericidal or inhibitory power.Therefore it may reasonably be assumed that the source of these elements is within the tick, but whether they are derived from the salivary glands or the stomach has not been shown. With regard to their nature, their action is not dependent upon the presence of alexin, and the lysin may be of the nature of an enzyme, or perhaps something similar to the “lysozyme” present in certain animal secretions, described by Fleming (1922). Both the lytic and inhibitory principles vary in amount in individual ticks, and neither is inactivated by exposure to a temperature of 58° C. for thirty minutes.

In all cases of ticks fed on bacterial cultures the micro-organisms remained within the confines of the alimentary canal, and no evidence of invasion of the haemocoele was found. Defaecation was the only process by which bacteria were found to leave the tick, and as only a few types were passed in this way, and defaecation occurs only at long intervals, and not as a rule during feeding, it seems very improbable that Argas persicus could be an efficient vector of any of the bacterial viruses employed in this work.