DEVELOPMENT OF A8CIDIANS. 



(Fig. 138, A, //) ; whether the primitive opening (Fig. 3S6 4 , 

 A, a] is closed or not, Kowalevsky says is an interesting 

 question. According to analogy with many other animals 

 it probably closes. 



The larva hatches in from 

 forty-eight to sixty hours af- 

 ter the beginning of segmen- 

 tation, and is then of the 

 form indicated by Fig. 386' 

 (copied with some additions 

 and omissions from Kupffer's 

 figure, being partly diagram- 

 matic). This anatomist dis- 

 covered in the larva of As- 

 cidia canina, which is more 

 transparent than Kowalev- 

 sky's Phallusia larva, not 

 only a central nervous cord 

 overlying the chorda dorsalis 

 and extending well into the 

 tail, while in the body of the 

 larva it becomes broader, 

 club-shaped, and surrounds 

 the sensitive cavity (), but 

 he also detected three pairs 

 of spinal nerves (.s) arising at 

 regular intervals from the 

 spinal cord (h, h') and dis- 

 tributed to the muscles (not 

 represented in the figure) of 

 the tail ; Kupffer calls / the 

 middle and g the lower brain- 

 ganglion. The pharynx (b), 

 or respiratory sac, is now 

 very large ; it opens pos- 

 teriorly into the stomach and 

 intestine (i) x represents 

 one of the three appendages by which the larva fastens 

 itself to some object when about to change into the adult, 



Fig. 386 6 . Larval Ascidian. a, sense 

 cavity containing the eye; b, pharynx or 

 respiratory sac ; c, notochord ; e, supposed 

 auditory organ ; /', middle, 17, lower brain- 

 ganglion ; h, ft, spinal cord ; ,s, s, s, three 

 sets of spinal nerves ; i, intestine ; <, 

 body-wall, consisting of epithelial cells. 

 Copied with some changes from Kupffer. 



