STUDIES ON THE PHOTOCHORDATA. 305 



the lower half of the 8 containing a lumen, while the upper 

 half is solid. In the next more anterior section (fig. 18) the 

 upper division of the 8 predominates over the lower, the lumen 

 of the latter being still of small diameter — in fact, rather smaller 

 than in the preceding sections ; while still farther in front 

 (fig. 19) the lumen, which is perfectly continuous all along, has 

 attained a relatively large diameter, while the superjacent solid 

 portion of the ganglion is correspondingly small, and is distinct 

 from the dorsal wall of the subjacent canal. In fact, fig. 19 

 represents a section through the funnel-like terminal dilata- 

 tion of the neuro-hypophysial canal spoken of above, which 

 may be called the hypophysial funnel; and the portion of 

 the ganglion involved in the section is its anterior extremity, 

 which has come to overlap the posterior portion of the funnel 

 (cf. the figures of young individuals of Ciona accompanying 

 " Studies,^^ &c.. No. I). 



Attention may be drawn to the ciliated prominence in the 

 wall of the branchial sac behind and below the hypophysial 

 opening in fig. 14. This is the epibranchial ridge (epibranchial 

 groove of Julin), which is grooved in many adult forms. It 

 is directly traceable to the projection caused in the dorsal wall 

 of the branchial sac by the pressure of the distended cerebral 

 vesicle in the larva (cf. figs. 9 and 12). 



Stage V. — The description which follows applies to the 

 relations of the neuro-hypophysial system in young immature 

 adults. 



Anteriorly the duct of the hypophysis expands into the large 

 funnel-shaped dilatation, which in its turn opens into the 

 branchial sac at the end of a papilliform prominence, which 

 projects boldly into the branchial chamber, and is continuous 

 with the epibranchial ridge referred to above. Fig. 20 shows 

 a section taken a short distance behind the branchial opening 

 of the hypophysis, and passing through the anterior dilatation, 

 above which are seen two cerebral nerves. Fig. 21 is drawn 

 from a section posterior to that of fig. 20, and show^ a great 

 decrease in diameter of the lumen of the hypophysis, while 

 still farther back the lumen becomes reduced to a minimum 



