1922] Reproduction of Hydra in Chapel Hill 93 



found without the spermaries also, and the ovaries are found only 

 in well-fed animals. 



The period, then, most favorable to sexual reproduction in Hydra 

 in this region begins in April and continues through May, and since 

 no cessation was noted at the time observations were discontinued, we 

 may conclude that it probably extends on into the summer. 



The course of the development of the egg in Hydra viridis was 

 followed in some detail. The egg arises from numerous ordinary 

 interstitial cells, which first enlarge beneath the epithelial ectoderm 

 and then coalesce to form a single egg. One nucleus persists as the 

 egg nucleus, the rest degenerate. The coalescence is at first by simple 

 fusion of the central cells to form a large central mass, which then 

 ingests the peripheral cells in an amoeboid fashion. 



My observations are in general accord with those of Jannreuther 

 (Biological Bulletin 14, 16) and Wager (Biol. Bull. 18). 



The subsequent development has been often described and is well 

 known. The time required for the development of the egg until its 

 extrusion through the ectoderm is about four days, while about three 

 weeks are consumed after the extrusion through the ectoderm before 

 the young hydra is hatched. These observations were made on animals 

 kept in laboratory vessels where it was also found that the number of 

 extruded eggs which fail to develop either from non-fertilization or 

 other causes is very large. It was not possible to determine whether 

 these same facts hold for the out-of-door environment. 



Chapel Hill, N. C. 



