Notes on the morphology of the Tunicata. 



501 



associate 

 ganglion 



Fig. A. 



themselves with the fibres of the rapheal nerve and are the 

 cells of this nerve. 



The point of chief interest in this species 

 is the presence in the raphe (at its base only) 

 of three distinct structures ; one the duct, derived 

 from the duct of the gland, and two distinct 

 nervous cords, one composed of fibres derived 

 from one of the atrial siphonal nerves, the other 

 composed of ganglion cells derived directly from 

 the brain. 



Fig. B. 



■.,..-gl- 



■ il' 



Fig. A. A dorsal view of tlie iutersiphonal organs of 

 Ascidia atra Les. This drawing is a reconstruction from 

 serial cross sections, c.f ciliated funnel, c.f accessory ciliated 

 funnel, d duct of neural gland, d' branch of duct of neural 

 gland, d.l dorsal lamina, which is continuous behind with 

 the upper end of the dorsal raphe, gg ganglion (brain), gl 

 neural gland, gl', gl", gl'" accessory glands, m longitudinal 

 muscle of the intersiphonal region, n nerve. 



Fig. B. A cross section through the ganglion and neural 

 gland of Ascidia atra Les., at the point marked // in Text- 

 Fig, A. yC^ 100 diameters. Reference letters as in Text- 

 Fig. A. 



