WITH NOTES ON THE WEST INDIAN SPECIES. 



255 



have become quite independent and their ducts occur a short distance removed from 

 the line of insertion of the lateral septum. The mature gonads do not exhaust the 

 entire capacity of the genital pleurae, but the distal free portion of the latter is left 

 free from gonads. The eggs are quite small, as they are in all Ptychoderidae, and 

 measure "15 mm. in diameter in the preserved state. 



Fig. 2. Portion of transverse section through genital region of adult Pt. carnosa ? ; showing lateral 

 accessory genital ducts. 



g. Gut-wall. Ig. Lateral divisions of the gonad. Is. Lateral septum, mg. Medial branch of gonad with 

 independent duct. x. Sterile border of pleural fold. 



Genito-hepatic Transition. 



The most characteristic feature of this transition, namely, the abrupt termination 

 of the genital pleurae (including the lateral septa), leaving a marked interval between 

 them and the anterior hepatic saccules, has been already mentioned and is clearly shown 

 in Fig. 6, PI. XXVII. ; this interval was even more pronounced in the living animal. 



In this species therefore the gonads do not encroach upon the hepatic region. 

 The wall of the gut in this region is thrown into a large number of folds arranged 

 with some regularity. In the anterior portion of the hepatic region there are two 

 specialised tracts of high, folded, ciliated epithelium, with basal nuclei and clear 

 periphery, placed symmetrically at the ventro-lateral borders of the gut. Whether 

 these remarkable tracts have any special significance I cannot say. I have not been 

 able to find in this region any ciliated apparatus like that described above in Pt. flava. 

 But I have (with difficulty owing to the extraordinarily folded wall of the gut) 

 ascertained the existence of the two ptychoderoid ciliated intestinal grooves in the 

 posterior hepatic and abdominal region. 



Caudal Region; Pygochord. 



The abdominal and caudal regions of this species are extremely flaccid, and there 

 is no external manifestation of the presence of a pygochord in the latter region, 

 w. III. 36 



