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Show 148 MR. A. E. SHirLEY ON T H E [June 16, unrecorded, but I should judge that they lay just under the peritoneal lining of the body-cavity. In one or two cases the worm itself was emerging, or had emerged, fi-om the cyst, but I attribute that to the handling the cyst received as the worms were removed from the body of the host. The cestodes usually were bent but once within the cyst, as is shown in the figure (PI. X V I . fig. 11). Sections through these cysts (PL X V I . fig. 8) show that the form in question belongs to Vaullegeard's second group founded on the type of Tetrarhynchus erinaceus van Ben., in which the larva? have a vesicle surrounding and protecting the head. This vesicle is clearly shown in the figure; within it the head of the larva and the neck, as far back as the muscular sacs into which the introverts are retracted, are coiled. These coils, being hidden by the vesicle, cannot be seen through the walls of the cyst; they are, however, sufficiently numerous to permit four or five sections of the head at different levels to be displayed in one section. The head passes into the body, which has two longitudinal excretory canals and shows no sign of reproductive organs ; in fact, the only differentiation from the loose parenchymatous tissue is a layer of muscle-cells situated about halfway between the periphery and the centre. The vesicle is folded over the head like an amnion ; it is, however, not closed, but remains open by a pore guarded by thickened lips. I a m inclined to think that these lips contain muscle-fibres, and that the aperture can be tightly closed if occasion arises. According to Vaullegeard the vesicle detaches itself when the larva becomes sexually mature. The genus Tetrarhynchus is often regarded as exclusively a fish parasite: it has, however, been described in certain Molluscs, e. g. Sepia officinalis and the Pearl-Oyster, and perhaps in Aphrodite aculeata, though nobody seems to have found it in that animal since the distinguished courtier, philosopher, parasitologist, and poet, Francis Redi of Arezzo, recorded it in 1664. I have found no record of the genus occurring in Echinoderms, so that the discovery by the Skeat Expedition of the larval forms in a Holothurian is a matter of considerable interest. This form, though not mature, is not enveloped in a vesicle, and presents certain features which allow m e to suggest a specific diagnosis. The second form brought back from the coast of Lower Siam is equally new as regards its host. There has hitherto been recorded, so far as I can find, but one vertebrate host of the genus Tetrarhynchus outside of the class Pisces. This is Testudo mydas, in which, in 1840, Meyer described vesiculate larvae. W e can now add a second Reptilian host in the case of Enhydrina valakadieu Boie, a sea-snake, belonging to the family Colubridse, which is not unfrequently taken along the coast of India and Burmah, and which ranges from the Persian Gulf to the Malay Archipelago and Papuasia. These very poisonous ophidians are fish-eaters. |