Development of Hydra a ml the Hydroidx. Ehrcnberg first showed 

 that the Hydra reproduced by eggs which ' become fertilized by 

 spermatic particles. Kleinenberg describes the testis, which is 

 lodged in the ectoderm and which develops tailed spermatozoa like 

 those of the higher animals. They arise, as in other higher ani- 

 mals, from a self-division of the nuclei of the testis-cells. There 

 is a true ovary formed in the same interstitial tissue of the ecto- 

 derm, consisting of a group of cells, which differ entirely in their 

 mode of formation from the ovaries (gonophores) of the marine 

 Hydroids, winch are genuine buds. 



It thus seems that Hydra is monoecious or hermaphrodite, i. e., 

 the sexes are not distinct. The egg of Hydra originates from the 

 central cell of the ovary; thus confirming the opinion now gener- 

 ally held that all animals as a rule arise from a simple cell. After 

 the egg-cell has escaped from the ovary through the ectoderm, it 

 still holds on by a narrow point to the sides of the Hydra, where 

 it is fecundated by the spermatic particles discharged into the 

 surrounding water from the testis. 



Fecundation is succeeded by a true segmentation of the egg.' 

 The young Hydra thus passes through a true " Morula" stage. 1 

 There is an outer layer of prismatic cells, forming the surface of 

 the germs, and surrounding the inner mass of polygonal cells. At 

 first none of these cells are nucleated, but afterwards nuclei ap- 

 pear, and it is an important fact that these nuclei do not arise 

 from any preexistent egg-nucleus. 



The next step is the formation of a true chitinous shell, envel- 

 oping the germ or embryo. After this Kh-inenherg asserts that 

 the cells of the germ become fused together, and that the germ is 

 like an unsegniruted egg. being a -ingle continuous mass of proto- 

 plasm. Allmun remarks that "as this phenomenon does not occur 



