EARLY DEVELOPMENT OF HYDRA. 



('72) as that o( H. aurantiaca, and by Brauer [op. cit.) as belong- 

 ing to H. grisea. It seems hardly possible that animals of both 

 species (assuming H. aurantiaca and H. grisea to be identical) 

 could have been taken under the same conditions and developed 

 to such numbers at the same time. If but one species was 

 present then it produced both forms of the embryo, while if both 

 were present then one must have entirely disappeared and given 

 place to the other. The latter alternative must have been attended 

 by a marked diminution in the number of the animals immedi- 

 ately following the first sexual period, and no such observation 

 was made. It appears then that the character of the embryo 

 cannot be taken as a constant and specific difference. Brauer 

 ('gifs:) uses this characteristic, together with the manner in which 

 the embryo leaves the body of the mother, in separating H. grisea 

 and H.fiisca: 



" Hydra grisea L. : Ei fallt ab. Form Kuglig, Schale ringsum 

 mit grossen, an der Spitze meistverzweigten Zacken besetzt." 



" Hydra fusca L. : Eier werden einzeln angeklebt, Form unten 

 flach, oben konvex, Schale nur auf der oberen Seite mit Kurzen 

 Stacheln besetzt." 



An explanation of the cause for this unusual embryo-formation 

 is not at hand. The conditions under which the spiculate em- 

 bryos were produced were, so far as one could observe, the same 

 as those under which the flattened, short-spiculate type were 

 formed. It is rather remarkable that during the eighteen months 

 and more^that the animals were kept under observation, only the 

 spherical, heavily spiculate embryos were to be found after the 

 first sexual period during which the alternate type was produced. 

 Moreover, the color of the animals under different conditions 

 varied greatly, as did also their size and disposition toward sexual 

 or non-sexual reproduction. Experiments were performed to 

 determine, if possible, the relation of color, size, and reproductive 

 proclivities to environmental factors. These were not altogether 

 conclusive, but will be presented in another paper. In general, 

 however, one may say that so widely do the animals vary under 

 different conditions that one might easily mistake for a different 

 species the forms encountered at either extremity of the varying 

 limit. This, it seems, will readily account for the numerous 



