66 Miscellaneous. 



The so-called blind lateral diverticula of the stomach, upon which so 

 much stress has been laid as a character peculiar to the ^ginidse, are 

 in reality only radiating gastrovascular canals, exceptionally widened 

 and flattened, opening at one end into the stomach and at the other 

 into the marginal canal. Lastly, those peculiarities of the tentacles 

 which have been indicated in the ^ginidse are met with in the pro- 

 visional tentacles of the Geryonidse. 



This remarkable discovery might, to a certain extent, have been 

 foreseen, by taking into consideration some isolated facts already 

 known. In 1853 KoUiker described, under the name of Stenogaster 

 complanatuSy a small ^ginide with sixteen rays, which he disco- 

 vered in the stomach of an ^Eginide with ten rays, Eury stoma rubi- 

 ginosum. In 1861 Fritz Miiller was led to suppose, from analogy, 

 that the Stenogastres were engendered by the Eurystomata. In 

 fact, he observed in an J^ginide of the BraziUan coast, to which he 

 gives the name of Cunina Kollikeriy that individuals octuply rayed 

 produced by gemmation in their stomach individuals covered with 

 vibratile cilia and duodecimally radiated. These facts, brought toge- 

 ther with that investigated by Hackel, show that in the iEginidse 

 there is a dimorphism of two sexual generations, one of which is 

 produced from the other by gemmation. 



Even the existence of spikes of Medusae, produced by the forma- 

 tion of numerous buds on the surface of the lingual cone of the 

 Geryonidae, is not so completely new as it might be thought at the 

 first glance. As early as 1 843, Krohn indicated an analogous spike 

 in the stomach of a Geryonia from the Mediterranean ; and in 1860 

 F. Miiller made a similar observation on a Brazilian Liriope ; but he 

 believed the spike to be of foreign origin, and to have been merely 

 swallowed by the Liriope, 



This singular mode of reproduction of the ^Eginidse evidently dif- 

 fers considerably from that prevailing in the other Hydroids. We 

 have nothing to do here with an alternation of one or several asexual 

 hydriform generations with a generation of sexual Medusae, but we 

 have a genetic union of two forms of sexual Medusae very different 

 from each other. In it M. Hackel sees a mode of generation essen- 

 tially different from the alternation of generations, and for it he 

 proposes the name of Alloeogenesis. Nevertheless this difference 

 is perhaps not so profound as it seems at the first glance. We must 

 indeed reject as forced the interpretation by which Mr. Allman 

 seeks to refer the exceptional facts observed by M. Hackel to the 

 normal form of the alternation of generations. Mr. Allman, in fact, 

 endeavours to make of the Geryonidae an asexual generation by 

 theoretically raising their generative organs to the rank of indepen- 

 dent zooids or rudimentary individuals of a sexual generation. Such 

 an interpretation seems to us to give an exaggerated importance to 

 the generative organs, each of which is really only a modification of 

 a radiating gastrovascular canal. In any case the existence of two 

 sexual forms in one and the same species is not now so surprising as 

 at the moment when M. Hackel wrote. The development of Ascaris 

 nigrovenosa, as revealed to us by the beautiful researches of MM. 



