The Ovogenesis of Hydra. 301 



food factor, the chance location of the germ cells must enter into 

 the problem. 



Number of Oyaries and Eggs. 



Individuals of all species of hydra produce fewer ovaries than 

 spermaries, as a rule. H. viridis usually produces but a single ovary, 

 according to Kleinenbeeg; the customary number is from one to 

 four or five in all the other species, a variability that is largely 

 influenced by the food conditions. The maximum time that this 

 reproduction may be maintained or the maximum number of ovaries 

 and eggs that may be produced by an individual, I do not know 

 and I have failed to find definite observations recorded on this point. 

 The longest period of Q^g production I have observed in a single 

 animal was sixteen days ; during this time the animal — ai/, fusca 

 — bore eleven ovaries and laid eleven eggs. Five ovaries was the 

 greatest number existing on it at any one time. The average 

 duration of an ovary was one hundred and three hours; the 

 temperature ranged between 36 and 82 degrees F. with an average 

 of slightly over 69 degrees. I have seen H. dioecia produce a larger 

 number of eggs, one individual laying seventeen eggs in seven days. 

 There were four ovaries on this animal. An ovary produces only 

 a single egg, rarely two, in H. viridis (Kleinenberg), H. fusca and 

 H. grisea but usually several in H. dioecia. 



The Formatiou of the Egg. 



Historical. Teembley briefly described and figured the egg and 

 embryo of hydra in his Memoir published in 1744. He says. — Mémoires 

 pour l'Histoire des Polypes, III. Mém. — "J'ai remarqué sur le corps de 

 plusieurs Polypes, des petites excrescences sphériques, qui y étoient 

 attachées par un peduncle fort court. Je n'en ai jamais vu plus de trois 

 à la fois sur le même Polype. Après être restées quelque tems attachées 

 aux Polypes, elles s'en sont séparées & sont tombées au fond du verre. 

 J'en ai observé à diverses reprises, avant & après leur séparation. Elles 

 sont toutes à la fin devenues à rien, excepté une seule, qui, peut-être, est 

 devenue un Polype." It was, apparently, the egg of H. grisea which he 

 saw. A few years later (1755), EoSEL V. EoSENHOFF figured the egg 

 of H. fusca. Pallas records (1766) actually seeing the young hydra 

 break out of the egg. Nearly a century passed without additions being 

 made to our knowledge of the egg of hydra ; on the contrary, during this 

 time, the opinion gained quite complete credence that the ovaries and 

 testes were of a pathologic character. In 1836, however, Ehrenbekg 

 gave a clear description of both eggs and sperm and so made it highly 



