148 MR. A. E. SHIPLEY ON THE [June 16, 



unrecorded, but I should judge that they lay just under the perito- 

 neal lining of the body-cavity. In one or two cases the worm 

 itself was emerging, or had emerged, from 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. XYI. fig. 11). 



Sections through these cysts (PI. XVI. fig. 8) show that the 

 form in question belongs to Yaullegeard's second group fotinded 

 on the type of Tetrarhynchus erinaceus van Ben., in which the 

 larv« 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 longi- 

 tudinal 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 am inclined to think that these lips contain 

 muscle-fibres, and that the aperture can be tightly closed if 

 occasion arises. According to Yaullegeard the vesicle detaches 

 itself when the larva becomes sexually mature. 



The genus Tetrarhynchus is often regarded as exclusively a fish 

 parasite : it has, howevei-, been described in certain Molluscs, 

 e. g. Sejna officincdis and the Pearl-Oyster, and perhaps in A2)hro- 

 dite 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 discoveiy 

 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 me to suggest a specific diagnosis. 



The second form brought back from the coast of Lowei- Siam 

 is equally new as regards its host. There has hithei'to been 

 recorded, so far as I can find, but one vertebrate host of the genus 

 Tetrarhynchus outside of the class Pisces. This is Testtodo mydas, 

 in which, in 1840, Meyer described vesiculate larvse.. We can now 

 add a second Keptilian host in the case of Enhydrina valakadien 

 Boie, a sea-snake, belonging to the family Colubridfe, 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. 



