W 1DIACEA — FORMATION OF ORGANS IN THE BUD. 



467 



The observations of van Beneden and Julin, made on the buds 

 of Chi "rl in, i, on the other hand, lead them to assume an ectodermal 

 origin of the neural tube. In early stages, this tube is closely 

 applied to the ectoderm and, in its posterior strand-like continuation, 

 the boundary between the ectoderm and the nervous system is quite 



Fio. 238. — Diagrammatic cross-sections through the posterior part of a bud of ' 'lavelina 

 (after vas Beneden and .Julin"). ep, epieardium ; ,</, genital vesicle; h, heart; i, 

 intestine ; m, stomach ; n, visceral nerve-strand ; oe, oesophagus ; pc, pericardial 

 vesicle; pk, posterior wall of the pharynx with the aperture of the oesophagus and 

 the paired apertures of the epicardial tube ; st, stolonic septum. 



obliterated (Fig. 238 D-F, n). [Seeliger (No. XXXIV.) has rein- 

 vestigated the bud of Clavelina, and finds that the nervous system 

 is unmistakably entodermal in origin, and in this conclusion he is 

 supported by Rittek's (No. XX VI 1 1.) investigation on Perophora, 

 one of the GlavelmidaeJ\ 



