ASCIDIA. 293 
Ascidia is hermaphrodite. The ¢esfes and ovaries are 
simple paired sacs lying over the stomach 
and leading by separate ducts into the atrium. 
The main interest attaching to Ascdra is involved in its 
development. If the anatomical account has been carefully 
Reproductive. 
Fig. 205.—DEVELOPMENT OF AN ASCIDIAN. 
(After KowALEvsk1.) 
Blastula. Gastrula. 
Blastoccele. 
Hypoblast. - 
Blastopore. 
—— 
Ts 
a 
re 
mecdGae 
sine 
Neural Tube. 
get 
oe 
5 
Peeodisn: 
xh 
The various stages are shown in median section. 
followed, it will have been noticed that Ascdza differs from 
nearly all the preceding types in having the 
nervous system confined to the dorsal region of 
the body, in possessing xumerous paired slits in the wall of the 
pharynx, and in the presence of a ventral heart, which is (in- 
termittently) respiratory, involving a backward current in the 
dorsal vessel and a forward in the ventral. ‘These are all 
characters in which the Zumcata resemble the other members 
of the important phylum C/ordata. In addition, in the 
structure of the pharynx, the method of feeding and the 
Development, 
