POSITION OF THE ASCIDIANS. 387. 
While all Tunicates, except Appendicularia, are more or 
less degenerate, losing their vertebrate characters, in Appen- 
dicularia these are retained. The heart is situated ventrally, 
occupying nearly the same relation as in Fig. 386’. Accord- 
ing to Claus, ‘‘the elongated cerebral ganglion is divided 
by constrictions into three parts; it is connected with a cili- 
ated pit and an otolithic vesicle, and is prolonged into a 
nerve-cord of considerable size. The latter is continued 
into the tail, at the base of which it swells out into a gan- 
glion; in its further course it forms several small ganglia, 
ne a BEES 
o ht spt 
spe 
Fig. 3862.—Diagram of larval Ascidian. Letteringas in Fig. 3861. m, mouth; 7, 
digestive tract; sp, spiracles in the pharyngeal portion; ht, heart; e, eye; er, ear; 
br, brain; ne, nervous cord; b’, b’’, mid-brain; cl, cerebellum; spn, spinal nerves; 
n, notocord; ol, nasal cavity; s, suckers (their homologues also occur in young 
garpikes and tadpoles). 
whence lateral nerves pass out. In consequence of a torsion 
of the axis of the tail, the originally dorsally-placed caudal 
nerve comes to have a lateral position. The segmentation 
of the nerve-cord in the tail (as shown by the ganglionic 
swellings) corresponds to the segmental divisions of the 
muscles, which recall the myotomes of Amphioxus. The 
large chorda (urochord), which extends along the whole 
length of the tail, constitutes another point of resemblance 
to Amphioxus.” * 
* Also see the treatises of Kowalevsky, Kupffer, Bateson, etc. 
