60 



HYDROZOA. 



an inch in diameter, with strong and thin walls, 

 which, when it was burst and the air expelled, fell 

 into sharp folds." 



Medusid^. — The development of the true J/e- 

 dusidce has yet to be effectively studied. From 

 the observations of J. Miiller on ^ginopsis, of 

 Gregenbaur on Trachynema and Gunina, 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- 



Fig. 12. 



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

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

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

 file, (a is slightly, b 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 



