500 MAYNARD M. METCALF, 



The secretion of the neural gland is formed by the disintegration 

 of cells proliferated from the endothelium of the gland. 



The duct of the gland is prolonged into the dorsal raphe. 



There is some indication of the innervation of the duct of the 

 gland near its point of connection with the ciliated funnel. 



It is well to call attention to the asymmetry of the rapheal nerve 

 (its origin), of the posterior siphonal nerves, of the rapheal duct (its 

 proximal end), and of the ciliated funnel (its position and form). 

 This will be referred to later. See page 523. 



The Cionas belong to the Cioninae, a sub-family of the As- 

 cidiidae. Of another sub-family, the Ascidiinae^ I have three represent- 

 atives — Ascidia mentula, Ascidia atra, and Phallusia mammillata. 



Ascidia mentula 0. F. M. 



Plate 34, Fig. 4. 



In this species, as is the case in most members of the sub-family 

 Ascidiinae, the ganglion and gland lie far back of the ciliated funnel, 

 the duct of the gland being very long. The funnel has the usual 

 horse-shoe form, with its ends asymmetrically coiled. The simple 

 duct connects, below the ganglion, with the gland, which is nearly as 

 large as the ganglion, and presents but one feature of special interest, 

 that is the asymmetrical position of its posterior portion. The anterior 

 part of the gland lies ventral to the ganglion, but its posterior end 

 pushes up on the right side. From the upper posterior corner of the 

 gland, the duct (r.d) continues upward and backward and inward 

 until it reaches the median plane of the body, here to bend down 

 into the dorsal raphe. From the upper posterior region of the 

 ganglion, not far from the base of this rapheal duct, there arises a 

 cord of ganglion cells (g.c) that pushes out to join the rapheal duct. 

 More ventrally, the cord and duct become indistinguishable owing to 

 the fact that the lumen of the latter becomes obliterated and its cells 

 disassociated, as if drawn apart. I have been unable to tell whether 

 the cells further down in the raphe are derived from the cord of 

 ganglion cells or from the duct or from both, apparently the latter. 



In addition to this cellular cord in the raphe, there is a well 

 defined nerve (r.n) which arises as a branch from the inner (ad- 

 mediau) side of the larger right posterior nerve and follows the 

 course shown in the figure. The rapheal nerve follows the rapheal 

 muscle almost to its ventral end near the oesophagus. The cells of 

 the cellular cord, after it enters the raphe, become loosely arranged and 



