404 



TUNICATA. 



(Fig. 199 A) shows that the inhalent aperture is wanting in the 



latter. The point at 

 ft j which we should expect 



it to lie is indicated 

 by i. It is evident that 

 the whole of the area 

 which corresponds to 

 the inhalent aperture 

 and the endostyle is 

 much abbreviated in 

 the Cyathozooid. The 

 stolon which, in com- 

 parison, is very highly 

 developed, thus appears 

 to be shifted forward. 

 We also find that 

 the atrial invagination 

 which appeared quite 

 at the anterior edge 

 of the germ -disc, actu- 

 ally corresponds to the 

 most posterior end of 

 the body of the Cyatho- 

 zooid and consequently 

 the terms "anterior" 

 and ' ' posterior " are 

 applied arbitrarily to 

 the germ - disc and 

 have nothing to do 

 with the orientation of 

 the Cyathozooid. 



FIG. 199. A, Diagram of a Pyrosoma embryo in the 

 stage of Fig. 193 A ; , diagrammatic median section 

 through a Salp (a solitary form), c, atrium; d, 

 alimentary canal of the Cyathozooid ; do, food-yolk ; 

 e, cloacal or exhalent orifice ; es, endostyle ; fl, 

 ciliated pit ; g, ganglion ; h, heart ; * (in R), inhalent 

 or branchial orifice, in A, the point at which it may 

 be conjectured to lie; r, edge of the germ-disc 

 growing over the yolk ; st, ventral stolon. 



E. Development of the four primary Ascidiozooids. 



The chain of Ascidiozooids, from the time it forms, contains 

 within it three longitudinal parallel tubes (Fig. 193), the middle 

 one representing the intestinal tube, the enteric rudiment of the 

 consecutive individuals, and the two lateral ones the peribranchial 

 tubes (p). These tubes are originally nothing more than direct 

 prolongations of the corresponding organs in the Cyathozooid (Fig. 

 192 B). When, at a later period, the individual Ascidiozooids 



