260 The Philippine Journal of Science wis 



From a study of the position of the nephridia of those forms 

 having only 1 pair of nephridia, it seems probable that that 

 pair represents the most anterior pair in those forms with 2 

 and 3 pairs and that in the differentiation from 3 pairs to 1, 

 first, the middle pair disappears and then the posterior pair. 

 Therefore, in this arrangement of the species of the group, it 

 has been divided; first, according to the number of nephridia 

 and, secondly, according to the arrangement of the muscles and 

 other less essential characters. 



In examining the various species of Thalassema which have 

 been described, 1 species is found which varies from the Thal- 

 assema type in such essential characteristics that I propose to 

 make it the type of a new genus, and possibly it ought to be 

 made the type of a new family. This is the species described 

 by Ikeda(20) as T. txnoides. Its most striking character is 

 its enormous size, its total length being some 2 meters. On 

 taking its internal structure into account, there are two very 

 deep lying and essential differences from the Thalassema type. 

 They are: first, the number and arrangement of the nephridia 

 and, secondly, the position of the longitudinal muscle in the 

 dermal muscle layer. In all other species of Thalassema the 

 nephridia are always in pairs or paired groups, the greatest 

 number of pairs recorded being 4, in T. decameron Lanchester; 

 and of paired groups, 8, in T. gogoshimense Ikeda. 



In this form there are an enormous number of nephridia which 

 are not arranged in pairs, but are scattered irregularly on each 

 side of the nerve cord. Ikeda says: 



They were never less than 200 in total number, and in certain individuals 

 I have estimated this to be nearly 400. Moreover, unlike all other known 

 Echiuroids, there is no indication of their segmental arrangement nor of 

 their strictly paired disposition. On the contrary, they occur densely and 

 irregnilarly crowded together in two longitudinal zones, one on each side 

 of the ventral nerve cord, beginning in front just behind the ventral hooks 

 and extending posteriorly to a length of 10 to 18 cm. 



Also, there are no spirally twisted internal openings, but all 

 the nephridia end in a terminal funnel. 



In all the Thalassema where descriptions of the dermal muscle 

 layer are given, the longitudinal muscle always is found lying 

 between the circular and oblique layers. In this species Ikeda 

 says that the muscle layers are as usual, but his figure of the 

 body wall shows that the thick longitudinal layer lies directly 

 under the corium and to the outside of both the circular and 

 oblique layers. 



