502 



MAYNARD M. METCALF, 



Ascidia atra Les. 

 Text-Figs. A, B, C and D. 



Ascidia atra differs from Ascidia mentula in several important 

 structural points. The ganglion is more elongated and slender. The 

 gland is very large, twice as long as the ganglion and about three 

 times as deep as the ganglion dorso-ventrally (Text-Figs. A and B). 

 I have found no other species in which the gland is so large in pro- 

 portion to the body. The upper end of the dorsal raphe is greatly 

 enlarged to accommodate the large gland (cf. Text-Fig. B). The duct 

 which leads forward into the ciliated funnel shows certain peculiar 

 features. At three distinct points (in each of the two specimens I 

 have had for study) the duct is associated with considerable masses 

 of glandular tissue (Text-Fig. A gV, gl", gl'"). In these accessory glands, 

 as in the main gland, the secretion is formed by the disintegration 

 of cells proliferated from the endothelium of the duct or its branches. 



Fig. C. A cross section through the duct of the neural gland of Ascidia atra Les., 

 at a point marked /// in Text-Fig. A. X 1*^^ diameters. Reference letters as in Text- 

 Fio-. A 



Between the anterior end of the large gland and the more an- 

 terior of the accessory glands, the duct gives off numerous branches, 

 which usually rebranch from one to five times, each twig ending in 

 a little ciliated funnel that opens into the peribranchial chamber 

 (cf. Text-Figs. A, C and D). There are one hundred and sixteen of 

 these accessory funnels in one specimen, and nearly the same number 

 in the other specimen. Each funnel has a round aperture with 

 flaring lips. 



