Vol. XIV. April, igo8. No. 4. 



BIOLOGICAL BULLETIN 



THE DEVELOPMENT OF HYDRA. 



GEO. W. TANNREUTHER. 



Introduction. 



The development of hydra has been described by Kleinenberg 

 (4), Kerschner (5), Brauer (3), and a few others, yet there are 

 many points of interest and importance that have not been pre- 

 sented, especially in the origin and formation of the ovary, in 

 fertilization and in early cleavage. 



The following results are based mostly upon one species : 

 Hydra sp.? (Brauer) or H. dicecia (Downing). The three forms 

 H. viridis, H. grisea ct7id H. fusca are universally recognized as 

 distinct species. Hydra sp.? (Brauer) has been observed by many 

 investigators, yet some prefer to consider it as a variety of H. 

 fusca. Brauer at first placed it with H. fusca, but upon discov- 

 ering that the sexes were separate, designated it as Hydra sp.?. 

 Downing (2) in his paper on " Spermatogenesis of Hydra " uses 

 the name H dicecia. 



Hydra sp.? (Brauer) which varies in color from a light to a 

 dark brown, resembles H. fusca. When we take into consider- 

 ation, however, that the sexes are separate, that the eggs are 

 glued to the object on which the parent rests by a secretion from 

 the ectoderm, and that the embryo may hatch out while the egg 

 is still attached to the parent form, it is perhaps justifiable to re- 

 gard it as a distinct species. 



Origin and Formation of the Ovary. 



The early formation of the ovary differs from Kleinenberg's 

 account as it is usually given in text-books. The interstitial 

 cells, which divide with nearly the same rate over the body of 



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