182 METAMORPHOSES OF MAN 



naturalist detected in Spongilla the distinction and 

 fundamental characters of the two sexes — the male 

 and female elements. The ova which he described 

 were clearly characterized by the existence of the 

 three concentric spheres, and were, according to him, 

 transformed at first into non-ciliated embryos. These 

 are the grains of the older writers, and the internal 

 germs of Laurent, who saw them, give rise directly to 

 spongillse. But a certain number, if not all of them, 

 undergo new modifications, become covered with cilia, 

 and thus by. travelling to a distance from their birth- 

 place, distribute the parent species. Bach of these 

 ova, therefore, is capable of producing, not only one 

 but very many individuals, which proceed indirectly 

 from it, but directly one from the other. Consequently, 

 we may class Spongilla, and doubtless all sponges, 

 among the animals which are reproduced by genea- 

 genesis. 



We may say the same, and with far greater reason, 

 of the Infusoria. 



The existence of the sexes in the Infusoria, the pro- 

 duction of ova in these microscopic organisms, and 

 especially the presence of the male element, have been 

 actively debated on many occasions. Ehrenberg, whom 

 we may call the re-discoverer of the world of micro- 

 scopic animals, admitted these three facts as the 

 results of his observations. On the other hand, our 

 skilful micrographer, F. Dujardin, who devoted himself 

 specially to the Infusoria, and who regards them as 

 composed exclusively of sarcocle, rejects the whole 

 three. 



Naturalists waver between these two extremes ; it 

 is quite true, as Messrs. Claparede and Lachmann have 



