METAZOA COELENTERA. Ill 



zoons. The first have long tentacles and supply nourish- 

 ing fluids to the whole colony, pouring them into the 

 cavity of the stem, the common reservoir from which the 

 swimming bells and other zoons draw. The sexual bells 

 are male and female and each female bell contains one egg. 



Apolemia (No. 150) is another float-bearing Siphono- 

 phore in which the polypstem has the covering scales 

 arranged in clusters with the tasters, feeding and repro- 

 ductive zoons. 



Abyla pentagona Esch. (No. 151), undergoes an addi- 

 tional process in the course of its development. Each 

 segment of the Siphonophore becomes detached and lives 

 an independent life. It is a feeding zoon with two loco- 

 motive bells for swimming, in which are the reproductive 

 organs. In this changed condition some of the parts may 

 become greatly altered in form. 



CTENOPHORA. 



The Ctenophora are interesting since they possess 

 characters in common with the Hydrozoa, the Worms, 

 and the Echinoderms. It may be they have arisen from 

 the Anthomedusan, Ctenaria ctenophora, and, if so, they 

 are the most differentiated of Medusae. On the other 

 hand, they have certain structures peculiar to the Turbel- 

 larian worms, while the possession of a digestive and 

 water vascular system in communication with each other 

 points to a relationship with the Echinoderms. 1 Accord- 

 ing to Chun, 2 the development of the egg of the Cteno- 

 phora is similar in the different genera, but the varia- 

 tions appear during the postembryonic development. 



The group is represented in the Collection by Pleuro- 



1 A. Agassiz, Mem. Amer. Acad. Arts and Sci., X, no. 3, 1874, p. 



379- 



2 Fauna und Flora des Golfes von Neapel, I, Leipzig, 1880. 



