WITH NOTES ON THE WEST INDIAN SPECIES. 



239 



Behind the last pair of gill-slits the gut still retains, over a distance of a few 

 millimetres, its division into upper and lower moieties corresponding to the branchial 

 and oesophageal portions. This fact has been already recorded for Pt. flava by Hill 

 (loc. cit. p. 343). A similar condition has been described by Spengel in Pt. erytkraea 

 {Monograph, p. 181, Text-figure) and more recently by Hill {loc. cit.) in Pt. hedleyi. 

 In Pt. erythraea Spengel describes the gut in this region as being divided " durch 

 zwei seitlich einspringende Falten in zwei Halbcanale, einen dorsalen und einen 

 ventralen." In Pt. bakamensis Spengel found the division to be a very unequal one, 

 the dorsal portion occurring as a rather deep furrow, while the ventral portion is much 

 more extensive. In Pt. hedleyi the dorsal moiety is very pronounced and is described 

 by Hill as a dorsal diverticulum possessing a transverse lumen and communicating 

 with the ventral portion of the gut "by a short, laterally compressed stalk"; its high 

 glandular epithelium is thrown into low folds. 



I shall refer to this dorsal portion of the gut at the anterior end of the post- 

 branchial genital region as the postbranchial canal (PI. XXVIII. Fig. 7). It is a 

 structure of some diagnostic and morphological importance. In Pt. flava new gill-slits 

 arise at the dorsal margins of the postbranchial canal at its anterior end. In Pt. hedleyi, 

 as described by Hill, and in Pt. ruficollis n. sp. (see below) it is quite independent of, 

 and dorsal to, the most posterior gill-slits. 



In Pt. flava the postbranchial canal occurs in direct continuity with the branchial 

 division of the gut. It is lined by a high, smooth deeply staining ciliated epithelium, 

 which passes rather abruptly into the folded epithelium of the ventral division of the 

 gut. Behind the last pair of gill-slits it possesses a narrow vertical lumen with a 

 slight dorsal dilatation, the lumen opening below, throughout its entire extent, into the 

 general cavity of the gut'. 



With regard to the formation of new gill-slits at the posterior end of the pharynx, 

 I observed in one series that the last gill-pouch of one side opens to the exterior, 

 while the corresponding pouch on the other side is present as a blind diverticulum 

 proceeding from the dorso-lateral margin of the gut, which has not yet come into 

 contact with the epidermis. Nevertheless the tongue bar has commenced to grow 

 down in the form of a slight vascular fold of the dorsal epithelium of the pouch- 

 like diverticulum. This early appearance of the tongue-bar before the perforation of the 

 gill-slit is a fact of impoi'tance and is in accordance with what Morgan- has observed 

 in Tornaria. 



In fact, whei'eas in Amphioxus the tongue-bars of the gill-slits are of secondary 

 origin and are therefore rightly referred to as the secondary bars, in the Enteropneusta 

 they are of primaiy origin, and should never be spoken of as secondary bars. 



Gonads. 



The gonads are essentially confined to the genital pleurae, and consist of a great 

 number of separate, more or less lobulated, genital glands, whose arrangement is on the 



1 In one specimen I found the cavity of the postbranchial canal to be wide and its walls somewhat 

 coarsely folded in contrast to the epithelial plications which occur in Pt. hedleyi and Pt. ruficollis. 

 - T. H. Morgan, "The growth and metamorphosis of Tornaria,'' Journ. Morph. v., 1891, p. 407. 

 w. III. 34 



