OPHIDIAN TAPEWOEMS. 



161 



course unarmed. The neck is long. The posterior proglottids 

 are longer than broad and from 2-3 mm. wide. The generative 

 pores alternate, but there are often as many as four or so 

 consecutively on one side. The external anatomy of this species 

 indeed hardly diflfers from that of Ophidotcenia naim, for which 

 I have recently founded the genus Ophidotcenia*. 



The internal structure, too, is very similar. In transverse 

 sections the calcareous bodies are by no means so plain as m 

 Ichthyotcenia gabonica just described. But in pieces of the body 

 mounted entire in glycerine the calcareous corpuscles are quite 

 obvious, and appear to be restricted to the lateral regions of the 

 segments, being absent or very few in the median dorsal and 

 ventral regions. It appeared to me that the glandular^ sub- 

 cuticular layer of the present Ophidotcenia does not consist of 

 such large cells as that of the other species of the genus. But the 

 arrangement of the longitudinal muscles was quite similar. It is 

 possible that the existence of the strong internal longitudinal 

 fibres in Ophidotcenia in the sexual proglottids and their very 

 feeble development in Ichthyotcenia gabonica, may prove to be 

 a generic distinction between these types. 



I could find in this worm only a single water- vascular trunk on 

 each side of the body. In this the two species of Ophidotcenia (if 

 there be two) agree ; but there is a small difi"erence to be observed 

 which helps to justify a separation. 



In the present species the water-vascular tube lies further away 

 (towards the centre of the proglottid) from the vitelline strip 

 than in Ophidota?nia naice. And this diff"erence is even greater 

 than appears by a mere inspection ; for the transverse diameter of 

 the sections of Ophidotcenia naice was greater than that of those 

 of Ophidotainia russelli. In the latter species I observed two and 

 a half to three ripe testes to lie between the water- vascular tube 

 and the vitelline strip, whereas there was only room for one or a 

 little more in Ophidotcenia naice. 



The reproductive orgcms also show some slight difierence in the 

 present species from what I have observed in its congener. The 

 testes are quite absent from the middle of the proglottids, and are 

 laterally pressed up close to the strip of vitelline glands. They 

 seem to me to extend further towards the middle line in Ophido- 

 tcenia naim. The cirrus-sac and the coil of the vas deferens 

 together reach to nearly the middle of the segment. The cirrus 

 is not by any means long and the coil within the cirrus-sac is 

 disposed in one or two loops only, thus contrasting with that of 

 Ichthyotmnia gabonica described above. It appears to me that the 

 coiled region' of the male duct lying within the cirrus-sac in 

 0-phidotcenia naice was rather larger than in the present species. 

 There is no doubt that the cirrus-sac is larger in the first-named 

 species. In any case, the small number of the coils lying within 

 the cirrus-sac of the present species contrasts very markedly with 



* P. Z. S. 1913, p. 25. 



