DEVELOPMENT OF ASCIDIANS. 



205 



(Fig. 138, A, li) ; whether the primitive opening (Fig. 138, 

 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. 139 

 (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 (a\ but 

 he also detected three pairs 

 of spinal nerves (s) arising at 

 regular intervals from the 

 spinal cord (h, li r ) and dis- 

 tributed to the muscles (not 

 represented in the figure) of 

 the tail ; KupfFer calls / the 

 middle and g the lower brain- 



o-MTio-lirm T>io Whom/riv Ch\ 

 gangllOll. me pliarynx (O), 



nr rpnirafr>rv PP i nnw 

 lespiratory Sac, IS nOW 



VPrv larcrp if rmpn<j nr>j 

 Vtry large , It OpCl , pOS- 



tei'iorly 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, 



139. Larval Ascidian. a, sense 

 ontaining the eye; ft, 

 respiratory sac ; c, notochord ; e, supposed 

 J 



cavity containing the eye; ft, pharynx or 

 otochord ; e, supposed 

 aiKitory 0rgan . f^ middle, g, lower brain- 



^ , , - 



ga n g'i n ; ^ A, spinal cord; s, #, a, three 

 *? O f spinal nerves ; j, intestine ; t, 

 body-wall, consisting of epithelial I cells.- 

 Copied with some changes from Knpffer. 



