26 ox A NEW SPECIES OF ENTEROPXEUSTA, 



pass from the limiting meml^rane of the epidermis through the 

 muscular layers to be inserted into the ventro-lateral portions of 

 the walls of the oesophagus and into the lateral regions of the gill 

 pockets. Laterad of the oesophagus a free space is left as in the 

 described species, and this contains in sections a coagulated fluid 

 in which cells are embedded. The two halves of the trunk coelom 

 are completely separated from each other ventrally by the ventral 

 vessel which extends between the limiting membrane of the 

 epidermis and that of the gut. On the dorsal side the dorsal 

 vessel may occupy the whole height of the mesentery or only its 

 dorsal half. 



Gut Canal of Branchial region: As in all the known species of 

 the genus Ptychodera the gut canal in this region is separated 

 into two passages — a dorsal or branchial canal (fig. 20, gg.) and a 

 ventral or oesophagus (fig. 20, ce.). The}' communicate with each 

 other by a narrower or wider cleft according as the two limiting- 

 cushions (fig. 20, Ic.) are approximated to or remote from each 

 other. Except for the much greater development of the genital 

 wings in this species, a transverse section through its branchial 

 region (fig. 20) agrees almost exactly with a similar section of 

 Ft. minuta. The gill skeleton is composed of three-pronged forks 

 which are related just as in Pt. minnta; the number of " Synap- 

 tikels " (fig. 20, an.) varies from seven to ten. 



The epibranchial stripe forming the median dorsal boundary of 

 the branchial canal is composed of numerous relatively very long 

 and narrow cells ; and its middle region does not stain so deeply 

 as the lateral regions in which gland cells are situated. The 

 lateral regions pass over opposite the "gill tongues" into the high 

 epithelium (fig. 21, gth.) of the "tongue back" (the inner wall of 

 the tongue next the gut canal). The gland cells are specially 

 abundant in the middle region of the epithelium of the "tongue 

 back," and not placed nearer its front face as in Pt. minuta. This 

 epithelium passes over into the narrow strand of "intermediate 

 epithelium" (fig. 21, ies.) composed of small non-ciliated cells 

 which furnishes the low epithelial covering of the "S3^naptikels." 

 The lateral walls of the tongue and of the gill pocket are lined 



