180 



ACTINOZOA. 



contractile, so as no longer to resemble those of 

 Pleurobrachia. Short branches are given off from 

 the extremities of the paragastric canals, and from 

 these the two canals which run by the sides of the 

 mouth are probably produced. Not until the large 

 lobes have become very distinctly recognizable do 

 the earlets, four small appendages in connection 

 with the lateral ctenophores, render themselves 

 visible. 



The observations of Semper on Chiajea multi- 

 cornis, another lobed representative of the same 

 order, indicate a still more rapid evolution of the 

 embryo, which before quitting its egg-covering 

 has the outward form of the adult animal, the 

 canal system and ctenophores being as yet rudi- 

 mentary. As in Bolina, the digestive tube appears 

 the first formed part of that system, and is, indeed, 

 developed earlier than any other internal organ. 

 At no period of its career is the young Chiajea 

 provided with a uniform covering of cilia. 



In Berne, a genus destitute of tentacles, the 



funnel of the embryo is comparatively large, before 

 the ctenophoral canals are fully developed. The 

 circular oral vessel is formed from two lateral 

 tubes, whose extremities anastomose with four of 

 the ctenophoral canals, while as yet the four others 

 have not approached more than half way the oral 

 pole of the body, towards which, as in the pre- 

 ceding, they are gradually developed. We have 

 here an interesting proof of the bilateral symmetry 

 of the Ctenophora, for in the adult Beroe, as from 

 its want of tentacles might have been expected, 

 this symmetry is, on a hasty inspection, less obvious 

 than in most other members of the order. 

 Like Chiajea, Pleurobrachia is developed within 





