ENTEROPNEUSTA FROM THE ABROLHOS ISLANDS. 97 



oesophageal. In Pt. bahamensis both divisions are nearly equal in area. In 

 Pt. erythrcea the branchial region is the smaller of the two, and this is the 

 condition in Ptycliodera pelsarti. The two cavities are not separated quite as 

 distinctly in the latter species as in the others named here. There is no 

 great constriction separating the two regions, which are consequently open to 

 each other by a rather wide channel. The line of demarcation between the 

 bases of the gills and the oesophageal epithelium is, as usual, marked by 

 longitudinal parabranchial ridges. They consist of epithelial cells which are 

 twice or more than twice as deep as the cells lining the rest of the 

 oesophageal division of the pharynx. 



The lateral septa of the genital pleura (PI. 11. fig. 11) bearing blood- 

 vessels, and connecting the gonads, arise as described by Willey in Pt. flava. 

 They are co-extensive with the genital pleura, and arise from the basement- 

 membrane close to the base of the gill-clefts. They are inserted into the 

 same basement-membrane near the free margin of the pleura. Behind the 

 pharynx there still seems to be some doubt as to the point of origin of the 

 lateral septa — Punnett and Spengel disagree with Willey. It has not been 

 possible to settle this question definitely from the slides at present at my 

 disposal. 



The gonads, as in Pt. flava^ are met so far anteriorly that they occur in the 

 same transverse sections as the collar canals. In other respects the repro- 

 ductive organs agree very closely with those of the other species of the genus 

 Ptychodera. 



Posterior to the gill-region the much reduced genital pleura encroach on 

 the hepatic region. 



Hepatic Region. 



The Hepatic Region is similar in structure to that of other species of the 

 genus. 



The epithelial wall of the alimentary canal is thrown into folds of con- 

 siderable irregularity, so that in transverse sections one meets "islands'^ of 

 " wall " on all sides. 



Two longitudinal grooves are present dorso-laterally, as in B. australiensis, 

 Pt. fiava, and Gl. hedleyi. 



The genital pleura can be traced into the hepatic region as very low 

 elevations just above the longitudinal grooves, a condition similar to that 

 described by Hill for B. axistraliensis. 



Caudal Region. 



Since Willey invented the term Pygochord for the ventral structure first 

 described by Spengel as a " Kielformiger Fortsatz " of the intestinal 

 epithelium, some little discussion has arisen concerning this feature. Willey 



