352 Miscellaneoufi. 



of the Hi/dra, which is thus, in its origin, a unicellular and eeto- 

 dermic formation. 



The granulations of a definitely formed ovum serve to produce 

 the larger elements which Ivleinenberg describes under the name 

 of 2)sendocells, 



After a detailed description of the segmentation, the German 

 naturalist passes to the formation of the blastoderm, as a pheno- 

 menon immediately succeeding the segmentation. The blastoderm 

 consists of a layer of cells, forming by itself the whole envelope of 

 the ovum. Kleinenberg regards the blastoderm as an embryonic 

 epithelium, taking no part in the ultimate formation of the Hi/dra, 

 but rejected like an envelope at a certain period of development ; 

 for this reason the adult Jli/dra is an animal destitute of epithe- 

 lium. 



My own investigations, which were carried on upon Hydra fusca, 

 completely contradict those of Kleinenberg. Nevertheless, in con- 

 formity with his researches, I have seen an agglomeration of cells 

 of ectodermic origin, which I regard as simply embryonic cells, 

 serving to reproduce different ectodermic elements. One of these 

 cells increases, and its nucleus is converted into a germinal vesicle. 

 At the same time the peripheral elements of the agglomeration 

 separate, forming a row of cells with small very refractive granules, 

 while the central cells unite to each other and to the enlarged cell ; 

 in this manner is formed a common plasmodium sprinkled with a 

 considerable number of nuclei. The germinal vesicle begins to be 

 degraded and disappears entirely (this last phenomenon agrees with 

 Kleinenberg's observations) ; but the nuclei of the central cells 

 undergo a transformation of another kind : they increase a little in 

 volume, and degenerate into fatty bodies ; at the same time some of 

 them divide (their nuclei also take part in this division). The 

 degeneration of a nucleus commences by a considerable increase of 

 its nucleolus, which becomes very refractive, and finally fuses with 

 the contents of the nucleus. It is these degenerated nuclei, which 

 probably serve for the nutrition of the embryo, that Kleinenberg 

 takes for pseudocells. The peripheral elements of the agglomera- 

 tion, sprinkled with granules of chitinous origin, serve to form the 

 shell (ecaille) or envelope of the ovum. 



Comparing my observations with those of Kleinenberg, I conclude 

 that the German naturalist has taken the peripheral cells of the 

 agglomeration for a blastoderm, and the mass of central cells for a 

 result of the segmentation of the ovum. According to my observa- 

 tions the Hydra must evidently not be regarded as an animal desti- 

 tute of epithelium ; my previous investigations * have proved that 

 this epithelium is muscular. — Coinptes Rendus, September 9, 1878, 

 p. 412. 



* Archives de Zoologie exp^rimentaJe, 1876 : " Histologie de I'Hydre 

 et de la Lucernaire." 



