26 
ON A NEW SPECIES OF ENTEROPNEUSTA, 
pass from the limiting membrane 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 vent rally 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, at.). They 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 Ft. minuta; the number of " Synap- 
tikels " (fig. 20, xn.) 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 g]and cells are specially 
abundant in the middle region of the epithelium of the "tongue 
back," and not placed nearer its front face as in Ft. 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 "Synaptikels." 
The lateral walls of the tongue and of the gill pocket are lined 
