4 RALPH E. WAGER. 



species described by the earlier investigators, who, naturally, 

 placed much emphasis upon color and size as specific differ- 

 ences. 



As killing agents, hot corrosive-acetic proved very satisfactory 

 when the preparations were to be stained with Heidenhain's iron- 

 hematoxylin. Corrosive subhmate, used both hot and cold, also 

 gave good results. Bouin's mixture proved especially valuable 

 in the study of the pseudo-cell formation. 



Origin of the Ovary. 



Most investigators of the problem of the oogenesis of Hydra 

 have attributed the origin of the ovary to the interstitial cells. 

 My own observations have agreed in this respect. Longitudinal 

 sections show that in the region in which the egg takes its origin 

 there are numerous nests of these minute cells, but in the lower, 

 or aboral end, they are much less numerous, and almost entirely 

 absent near the foot. They are often found dividing mitotically, 

 when there are usually three or four divisions taking place very 

 near together. They vary somewhat in size in different sections, 

 but their appearance and disposition would lead to the following 

 conclusion with regard to their growth. 



The very young interstitial cell is possessed of a nucleus which 

 has a very delicate chromatin reticulum with small nodal enlarge- 

 ments. The nucleus, to a great degree, fills the whole cell, there 

 being but a very thin envelop of cytoplasm. With the onset of 

 ^gfe production, the nucleus begins to enlarge and very soon a 

 definite nucleolus can be found, and not infrequently, two are pres- 

 ent. The mass of the cytoplasm increases at the same time and 

 as a result of this increase in the size of these cells, a layer of the 

 primative ova, as they have been called, is definitely established. 

 Externally, this is evidenced by the clitellum-like enlargement 

 usually in the upper third of the body. This sometimes com- 

 pletely surrounds the body, or, with perhaps equal frequency, is 

 found on one side only. Cases were noted in which no marked 

 change in the external appearance could be seen, yet the process 

 of &^^ production took place. The size of the o.^^ is dependent 

 in part upon the quantitative production of these cells, as will be- 

 come evident from the discussion of their fate. Whether or not 



