Ransom and Foster have published a preliminary account of experiments on the life history of Ascaris lumbricoides in the Journal of Agricultural Research of 19th November, 1917. They found that a repetition of my experiments on the feeding of rats and mice with ripe Ascaris eggs gave results agreeing very closely with those recorded by me in the British Medical Journal of July 1st, October 7th and December 2nd, 1916, and in Parasitology of February 1917.

During the months of September, October, November and December 1917 I collected 1250 different specimens of fresh-water snails from various parts of the Transvaal, more especially from the sources of the Vaal and Crocodile rivers. All the larger specimens I submitted to microscopic examination for possible infection with cercariae. From the mud at the bottom of the Mooi river at Potchefstroom, which is a tributary of the Vaal, I came across some very finely preserved specimens of Unio caffer Krauss, a large number of which contained small pearls attached to the shell. The amount of lime in the bed of this river probably accounted for the perfect state of the umbones of these Uniones. Amongst the small stones at the bottom of the river I collected some remarkably large specimens of Corbicula radiata Parreyss. The river also contained some specimens of Pisidium, a much smaller variety, not yet identified. On the decomposing rushes at the edge of this river there were numerous specimens of Ancylus, for which Mr Henry C. Burnup has suggested the name Ancylus cawstoni; I have seen similar specimens at Klerksdorp and in the Hex river at Kustenburg, a branch of the Little Crocodile. All these specimens were free from cercarial infection.

Three kinds of lice are found on horses, two belonging to the Mallophaga or scale-eating lice and one to the Siphunculata or blood-sucking lice.

In my previous paper on the body louse (1916) many points of morphological interest were necessarily left in abeyance and mention was made that certain statements in it were open to correction. Further work has rendered correction possible. While working in France, to ascertain whether Pediculus humanus was a carrier of the spirochaete of Weil's disease, opportunity was taken to investigate those organs of the louse in which the spirochaete might lodge and the afferent and efferent channels through which it might pass. The enquiry did not demonstrate the presence of the spirochaete in the body louse, but incidentally a detailed knowledge of the mechanism of feeding was obtained and is here presented. Since the main conclusions of this paper were reached (December, 1916) I have read Harrison's paper, “A Preliminary Account of the Structure of the Mouth-Parts in the Body-Louse,” and while much of the following verifies his statements, we differ on certain important points regarding the structure of the mouth-parts and musculature.

The animal under consideration belonging to the family Lernaeopodidae was taken on a codling (Gadus morrhua), 13 ins. in length, caught at Plymouth several years ago, and preserved in formalin since that date. Although about twenty-six valid species of Clavella have been either recorded or described in detail, the subject of the present paper differs from them all in combining several of the more prominent characters of other species, notably the extreme length of the backwardly-arched cephalothorax taken together with the reduction of the “arms” (second maxillae) and their expansion into a disc so that the “bulla” or button appears to be almost directly affixed to the body. For this species I accordingly propose the name Clavella sciatheric.

p. 225, line 12, read 0·5 (caustic soda 0·5 pt.) for 5

Amblyomma hebraeum males anchor immediately when placed in a hungry state upon the host. The females will not do so as a rule in the absence of previously anchored males. Usually the males do not move or scarcely move when once anchored on the host, they may continue to remain attached to the host for months after the females have dropped off gorged. The males, after having fed for a few days, show signs of sexual excitement in that they erect their bodies away from the host and extend their legs, whereby, without releasing their mouthparts from the host's skin, they seize and hold any females that chance their way. The males become excited when the skin of the host in their vicinity is handled, no females having been near them for months. To copulate, the males must necessarily release their mouthparts, and this may at times lead to their shifting their position. They may occasionally shift to a fresh anchorage in company with their females, or they may shift a few mm. when apparently alone. A male may copulate with several females. The coloration of the male changes after prolonged sojourn upon the host (77–141 days).

After feeding for 2–8 days or more, the females wander and are grasped by anchored males so that the ticks' ventral surfaces are apposed, and in this position the female proceeds to feed with her mouthparts puncturing the skin of the host in close proximity to those of the male. Copulation takes place in due course, the male temporarily removing his mouthparts from the host for the purpose. A female may seek two males in succession but usually one male appears to suffice. Females feed very slowly in the absence of males, they gorge rapidly when fertilized, and, when fully gorged, usually abandon the host without delay. Depending upon their having access to males and access to a more or less adequate food supply from the host, the females remain upon the host for 4–25 days before dropping off in a gorged condition.

Hyalomma aegyptium males anchor immediately when placed upon the host. In the absence of females they remain fixed or change their position but slightly at long intervals of time. When hungry males and females are placed together upon the host, they proceed to suck blood at once, and, after a preliminary feed lasting five or more days, the males wander in search of females. A male may copulate with several females. Females placed in close proximity to males cause these to become excited (as in A. hebraeum). The females as a rule do not change their anchorage upon the host from start to finish, being sought by the males. The latter stay upon the host indefinitely (122 or more days) after the gorged and fertilized females have dropped off.

Rhipicephalus bursa males and females, when hungry, proceed to feed at once when placed together upon the host. After remaining fixed for 3–5 days, the males seek anchored females. The males may seek a number of females in succession, usually feeding for some days prior to seeking a fresh female. Males continue to wander from anchorage to anchorage in the absence of females, they may thus wander about for 86 days or longer after the females have abandoned the host. A male may copulate with several females.

The behaviour of the sexes differs therefore in the three foregoing species. In A. hebraeum the females seek the males, in H. aegyptium and R. bursa the males seek the females. In all three species the males remain upon the host indefinitely after the females have dropped off. In R. bursa the males continue to wander about from anchorage to anchorage long after the females have left, whilst in A. hebraeum and H. aegyptium the males stop their wandering entirely or shift but slightly at longer intervals of time.

The predominance of male ticks of any species upon a host under natural conditions is accounted for by their staying on and accumulating upon the host whilst successive lots of females drop off. As an example I may mention that I have seen camels in Biskra on which only males of H. aegyptium could be found; these males must have been a very long time upon the camels because their scutums were polished and scratched, the rugose surface so characteristic of the young male tick having been worn away.

Copulation in all three species was observed on several occasions upon the host, the process lasted 10 minutes or longer and was similar to that described by me for Ornithodorus and Ixodes.

Since the liability to injury increases with the degree of engorgement of the female tick it is a great safeguard to her that she attains her full state of engorgement rapidly at the end of her feeding period and that she drops from the host promptly.

The cestodes of lizards have received little recent attention from systematic zoologists. Those inhabiting snakes are much better known than they were a few years ago, thanks to the researches of La Rue (1914) and of Rudin (1917). The cestodes of snakes almost all belong to the family Ichthyotaeniidae (genera Crepidobothrium, Ophiotaenia, Acanthotaenia). Among the lizards also, several species of Acanthotaenia occur in the Monitors (Varanus), and one is recorded in Lialis, one of the Pygopodidae. The Monitors are also the hosts of a remarkable genus of quite a different type—Duthiersia—our knowledge of which has recently been brought up to date by Beddard (1917), and of another genus—Pancerina—of an equally distinct type.

The actual commencement of the great wave of human trypanosomiasis, which claimed so many thousands of lives along the shores of Lake Victoria, is difficult to determine. The attention of Europeans was first attracted to the disease early in 1901, when eight cases of sleeping sickness were admitted to Mengo hospital by the Drs Cook, who had been established in Uganda some five years, to whom the clinical picture was quite new. Enquiry among the chiefs of Buganda revealed the fact that sleeping sickness was known to the natives as mongota, and was more prevalent in the eastern portion of the Protectorate than in Buganda itself. A large number of deaths had already occurred in Busoga Province and in Buvuma Island.

This paper consists of two parts: (I) a complete account of the life-history and a description of early stages of Melinda cognata Meigen which I found here in Cambridge living as parasites on a common snail, Helicella virgata da Costa, and (II) a review of all observations made hitherto on the life-history of different flies feeding upon living or dead molluscs.

The investigation, of which the results contained in this paper are a part, was first commenced in 1910. It was then proposed to describe in some detail the entire anatomy of the adult insect, but when a measure of progress had been made, and the alimentary, tracheal, and nervous systems had been almost completed, the work was interrupted by my taking up an appointment in India. On returning to England in 1915, the enquiry was resumed for a short period at the end of the year, but early in 1916 it had to be abandoned again to meet the superior claims of entomological work with the Forces in Mesopotamia, for the War Office. This, and other investigations connected with problems which have arisen in England in consequence of the War, prevented any further progress being made, but, with the declaration of the Armistice it was felt that attention might once more be given to it. In the limited time which could be devoted to the work, it has not been possible to carry out the original plan of including the whole anatomy in one paper, and the description of the head and mouth parts has been selected because of the somewhat novel considerations which have arisen in connection with the latter, particularly with regard to the function of the labium during the operation of piercing, the publication of which it seemed undesirable to delav further.