CNIDARIA 



59 



Metschnikoff (No. 12) has described and designated as sjwrogonia a 

 remarkable method of reproduction in Cunina proboscidea. This would 

 be the only case of parthenogenetically developing eggs among Coelen- 

 terates. There are developed in the sexual organs of this form (in 

 addition to the reproductive elements) neutral amoeboid sexual cells, 

 which soon migrate out of their places of origin and penetrate into the 

 entoderm of the gastral pockets and of the ring-canal, and also into the 

 gelatinous layer of the sub-umbrella. These amceboid cells, which occur 

 in males as well as females, at first divide, and then one of the cells 

 closes around the other. The enclosed cell is converted into the embryo, 

 while the enveloping cell, as an enormously enlarged amceboid cover- 

 cell, provides for the nutrition, the motion, and the attachment of the 

 embryo. With the further growth of the ciliate embryo it hangs free in 

 the gastral cavity of the parent animal, while the cover-cell alone effects 

 the attachment to the entoderm. Finally, the embryos become free in 

 the gastral space of the parent, where they are metamorphosed into 

 medusie, and at the same time produce buds from their aboral pole. 

 The medusffi thus i^roduced are already sexually mature at the moment 

 of their emergence from the body of the parent. They are, however, 

 essentially different from the parent. They have the characters of the 

 Solmaridffi in so far as they possess a simple gastral sac and a ring- 

 shaped gonad, whereas " otoporpfe " are wanting. Here, therefore, 

 there is an alternation in the cycle of development of two differently 

 constructed sexual generations, one of which has arisen in a partheno- 

 genetic manner (or by budding). These conditions require further 

 investigation and confirmation. 



II. SiPHONOPHORA. 



Systematic : I. Physophoridas. 



1. Physonectse (Haeckel). 



2. Pneumatophoridse (Rhizophysa, 



Physalia). 



3. Tracheophysae (Vellela, Porpita). 



II. Calycophoridae. 



The eggs of the Siphonophora are developed in sessile 

 gonophores, oi' in small, ultimately free, primitively quadri- 

 radiate craspedote medusa, and are fertilized in the sea- 

 water after their deposition. They are spherical, usually 

 naked (with the exception of Hippopodius gleba), and re- 

 semble the eggs of the Greryonidse and Ctenophora in so 

 far as a dense homogenous exoplasm and a vacuolated, 



