98 SYNOPTIC COLLECTION. 



to one of the Geryonids, remains a hydra, while its buds 

 develop into medusae and swim away. Here, then, we 

 have the metamorphosis of Aeginopsis converted into the 

 alternation of generations so peculiar to this class of ani- 

 mals. 



The objection may here be urged that the genus Cunina 

 is parasitic or semi-parasitic in habit and that therefore it 

 is a specialized and reduced genus. The stock form 

 Aeginopsis, which is the key to our classification, is not 

 a parasite at any period of life. Cunina octonaria does 

 not seem to be much more of a parasite than an animal 

 that happens to settle upon something, it may be another 

 animal or a rock, for a short time. It is free at first, then 

 attaches itself to an animal for a brief period, and after- 

 ward lives an independent life. The species Cunina par- 

 asitica is a parasite, as its name implies, but it illustrates 

 so admirably what seems to us the next step in the evolu- 

 tionary development of this class of animals that we use 

 it provisionally, until at least a non-parasitic form can be 

 found which will illustrate the same type of life history. 



HYDROPHORA. TRACHOMEDUSAE. 



The Trachomedusae are represented in the Collection 

 by Carmarina ( = Geryonia) hastatalAld. (No. 115), which 

 corresponds to Aeginopsis among the Narcomedusae in 

 passing through a metamorphosis without budding or 

 alternation of generations. It is an interesting fact that 

 the larval Geryonidae have solid tentacles, while in the 

 adults these are replaced by hollow ones. The Tracho- 

 medusae include Aglaura whose complete development 

 has been worked out by Metschnikoff. PL 116, fig. i is 

 the fresh laid egg drawn from life; fig. 2, the same treated 

 with osmic acid ; fig. 3 shows the beginning of .segmenta- 

 tion ; fig. 4. the egg divided into two cells; fig. 5, the 

 four celled stage ; fig. 6 is the third furrowing stage from 



