60 



HYDROZOA. 



an inch in diameter, with strong and thin walls, 

 w^hich, when it was burst and the air expelled, fell 

 into sharp folds." 



Medusidm. — The development of the true Me- 



dusidce has yet to be effectively studied. From 

 the observations of J. Miiller on jEginopsis, of 

 Gregenbaur on Trachynema and Cunina, and of 

 Fritz Miiller on Liriope, it seems highly probable 

 that these genera proceed at once from the con- 

 dition of the embryo to assume the aspect of the 

 organism which gave them birth. Still more con- 

 clusive on this point are the results of some recent 

 researches of Claparede on a Medusid closely 

 allied (if not belonging) to the genus Lizzia. 

 Within the substance of the body- wall of the de- 



Fiff.v. 



Development of Lizzia: — a, adult Lizzia, the walls of whose 

 polypite are seen to bear numerous ova ; b, supposed free-su-im- 

 ming young of a, viewed from below ; c, the same, seen in pro- 

 file, (a is slightly, h and c are very much, magnified.) 



pendent polypite were observed numbers of what 

 seemed to be true ova, some furnished with germ- 

 vesicle and germ-spot, others in a more advanced 

 stage of development. These last resembled in 



