:;'.t. 



TUNICATA. 



The transformations undergone, in the further course of develop- 

 ment, by the paired coelomie sacs, the lumina of which had become 



T.C. 



Fig. 191. -Three germ-discs of Pyrosoma, diagrammatic (after Salensky). d, enteric' 

 cavity; es, endostyle ; Ic, left coelomie sac ; n, rudiment of the nervous system ; 

 p, peribranchial tubes; pc, pericardial sac = re, right coelomie sac. 



connected posteriorly, are of importance. Only the right coelomie 

 sac is retained (Fig. 191, re), while the left* undergoes degeneration 

 (Fig. 191 A-C), its lumen becoming smaller and its cells losing their 



- .es 



en 



'IV I ^-~ 1 .T embl y° s " f Pyrosoma (after Kowalevsky). cl, atrial aperture of the 

 yatnozooid. en, eudostyle-folds ; n, nervous system ; o, aperture of one of the peri- 

 bran ehial tubes ; p, peribrauehial tube ; pe, pericardial sac : pc', posterior tubular 

 continuation of the pericardial sac ; ... posterior pari oi the germ-disc raised up from 

 the surface oi the egg (rudiment of the stolon) ; -.. .-ell-zone'. 



i 'l'-™:," ngh \ and " left " refer t0 the arrangement of the organ., in 



he adult < yathozooid, in whirl, the atrial aperture denotes the posterior end 



oi the body. Asm our orientation of the germ-disc, the atrial aperture lies 

 I : ho anterior edge of the disc, the right and left organs appear to be reversed. 



Our orientation of the germ-disc is. however, intentional (p. 404), having been 



retained in accordance with the views of authors, since the opposite orienta- 

 wouhl also lead to certain difficulties in describing .he processes (especially 



m connection with the development of the Ascidiozooid). 



