ENTEROPNEUSTA HILL. 341 



The inner concave wall of the gill tongue ("tongue back") is 

 composed of the usual high epithelium, in the anterior and posterior 

 faces of which small flask-shaped gland cells occur (fig. 10, gib.). 



The first gill pocket lies under cover of the posterior end of the 

 collar, and as has already been mentioned, the first and second 

 pockets have a common efferent portion which opens to the ex- 

 terior between the collar and trunk by a narrow slit-like canal 

 (Plate xx., fig. 8, gp. 1 and 2). 



The gills in one of the larger specimens of this species with a 

 gill area measuring 3 cm. in length, would number considerably 

 over one hundred pairs. 



The usual septa and gill tongue vessels are present (Plate xxi., fig. 

 10). The dorsal vessel in this region occupies only the dorsal half of 

 the dorsal mesentery, and the afferent gill vessels' diverge about 

 opposite the gill tongues outwards and downwards from its ventral 

 side as in P. minuta. As Spengel describes, each afferent vessel 

 stands in direct connection with the two vessels in the gill tongue 

 lying one on each side just within the tongue bars of the gill 

 skeleton, and also in connection with a septal vessel, apparently 

 in this species with either the septal vessel of the septum in front 

 of, or behind the corresponding tongue. The capillary system of 

 the gill tongues also appears to stand in connection with the 

 septal vessels by connecting branches running round the dorsal 

 ends of the gills. 



In this species these leave the ventral side of the dorsal vessel, 

 not only the afferent branchial vessels, but also branches which 

 pass to the mesial wall of the efferent portions of the gill pockets 

 (fig. 9). 



Towards the posterior end of the branchial region the median 

 dorsal groove becomes much shallower, while the branchial grooves 

 become markedly wider and deeper. The median dorsal portion 

 of the body in the region of the developing gill pockets thus forms 

 a prominent longitudinal projection in which the branchial canal 

 is situated, while the dorso-lateral portions of the body stand out 

 as thick free wings. The gill pores here open near the middle of 

 the mesial wall of the widened branchial groove, while the genital 

 pores open on its lateral wall, about on a level with the gill 

 pores. 



Genital Region. Intheanterior portionof this region, just behind 

 the last developing gill pockets, the alimentary canal of P. hedleyi 

 exhibits a noteworthy differentiation into two portions similar to 

 and perhaps even more marked than that described by Spengel 

 for the corresponding portion of the intestine in P. erythrcea and 

 P. bahamensis. 



