420 



EMBRYOLOGY 



and 199 B). Of these the latter is much the longer (Fig. 200 

 A to D). 



By the bulging and growing outward of the peripheral 

 parts of the larva, there arise longer and shorter processes, 

 which are bordered by the ciliated bands (Fig. 200 G). This 

 larval form received from its discoverer, Sars, the name of 

 ^^ Bipinnaria'' (asterigera), which it continued to bear even 

 after its relation to the starfishes was recognized. 



Fig. 200.— Development of the Bipinnaria and Brachiolaria from the funda- 

 mental form of the Echinoderm larva (diagram afterJoH.MiJLLEK, from Balfoxir's 

 Comparative Embryology). The broad black line indicates the ciliated band, the 

 shaded part the depressed portion of the surface. (Comp. footnote on p. 417 in 

 regard to the orientation of the figures.) an, anus; m, mouth. 



The opinion which Semon advances concerning the origin of the Bi- 

 jnnnaria larva does not agree with the description of it which we have 

 just given, Semon finds in the Echinoderm larva a ciliated band surround- 

 ing the mouth, a loop of which occasionally extends into the oesophagus 

 (as in the Auricularia). This " adoral " ciliated band has nothing to do 

 with the continuous ciliated band, but exists independently of it. In the 

 Bipinnaria the "adoral" ciliated band of Semon is said also to supjjly 

 that part of the ciliated band which we called the adoral part, so that the 

 latter is not, as we described it, to be looked upon as a detached part of 

 the continuous ciliated band. As long as strict proof of such a mode of 

 origin is not forthcoming, we are unable to accept this opinion. The 

 agreement of the preoral area in Auricularia and Bipinnaria is too 

 striking for one not to assume that its isolation took place by means of 



