of Dist aplia do not stand in the slightest agreement with 

 any of those obtained for Bo_tryllus. The nervous-syste.'n of 

 the Distaplia-bud is of ectodermal origin, according to him. 

 Cells sink down at a very early period from the ectodermal 

 wall, and form a solid mass, which later acquires a cavity, 

 increases in length, and produces a tube. The latter be- 

 comes differentiated into three parts; the anterior gives 

 rise to the hypophysis, the middle to the ganglion, and the 

 posterior portion to the visceral nerve. The hypophysis and 

 ganglion have, therefore, a common origin. This mode of 

 formation, however, is only true of the primordial bud; for 

 all the other buds, which are produced from it by fission, de- 

 rive their nervous-system by division directly from that of 

 the parent along with the rtst of their organs. 



Tt might be mentioned that in the buds of Pyrosoma, 

 Salensky (26) has described a similar ectodermal origin of 

 the nervous-system, although Seoliger (30) in the same form 

 aerives the common rudiment of ganglion and hypophysis from 

 mesodermal cells. 



Salensky's results on Distaplia are directly con- 

 tradicted by Hjort and Frl . Bonnevie (10). The latter find 

 no trace of the nervous-system in the early stage at which 

 Salensky describes its first appearance, but maintain, on the 

 contrary, that a forwardly directed diverticulum is later 

 formed from the dorsal wall of tne inner vesicle, just as in 

 Botryllus, and that the ganglion is differentiated from the 

 wall of the dorsal tube. 



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