SOME BIPINNARM FROM THE ENGLISH CHANNEL. 459 



This loss has obviously been brought about by the assumption 

 of burrowing habits after the ancestor of Balanoglossus 

 ceased to lead a pelagic life. The existence of Asterid larvae 

 in which the prae-oral lobe is specially developed for the pur- 

 pose of swimming in the open sea seems to me, when the close 

 similarity of Torn aria with a simple Asterid larva is taken 

 into account, to point to the idea that the pelagic ancestor of 

 Balanoglossus was also provided with a muscular and flex- 

 ible prae-oral lobe bounded by the two ciliated bands, and used 

 for swimming. In Balanoglossus, after the adoption of life 

 upon the sea bottom, the prae-oral lobe, developed under 

 pelagic influences, was used for moving about in the mud, 

 and rapidly lost its primitive ciliated bands under the new 

 conditions. 



LiTERATTJBE. 



KoKEN ET Danielssen, — " Sur la Bipinnaria asterigera," *Aun. 

 des Sciences Naturelles,' 1847 (3), vii, pp. 347—352, pi. vii. 



MiJLLEB, Johannes. — "Ueber die Larveu u. die Metamorphosen der 

 Echinodermen," ' Abh. d. k. Akad. Wiss./ Berlin, 1850, pp. 81—94, 

 pi. ii; 1851, pp. 61 — 65, pi. vii. 



Sars, M. — ' Beskrivelse og lagttagelser over nogle moerkelige eller nye 

 i Havet ved deu Bergenske Kyst levende Dyr.,' Bergen, 1835, pp. 

 37, 38, pi. XV. 



