594 SHEINA MARSHALL 



these conditions the Hydras hved and remained healthy for 

 months. Occasionally one or two, for no apparent reason, 

 would decrease in size and finally degenerate and die, but in 

 only one case was a whole tumbler attacked by a ' depression 

 period '. Even here a fair proportion remained healthy 

 throughout. When well fed the Hydras budded actively. 

 None of my specimens carried more than four or five buds 

 at a time and the number was usually less. 



Sexual reproduction took place in autumn and in early 

 summer. The animals were hermaphrodite. With the excep- 

 tion of four specimens, not differing outwardly from the rest, 

 all those which produced eggs produced testes at the same 

 time. Testis formation usually began before egg formation 

 in any individual. Many specimens showed testes without 

 eggs, but as egg production entails a considerably larger 

 expenditure of energy and food material than testis produc- 

 tion, this is not surprising. The four exceptional, apparently 

 female, specimens were kept under observation for about eight 

 weeks, but died before undergoing another sexual period. 

 Three or four eggs were sometimes formed at one time, although 

 they might not all attain full size and break through the 

 ectoderm. 



One large and healthy specimen showed four eggs developing 

 and a number of testes. Three of the latter had developed in 

 the ectoderm of three tentacles. One testis w^as just at the 

 root of a tentacle, another a little further out, and the third 

 at a distance from its base of about quarter the length of the 

 tentacle. The testes were ripe and spermatozoa were swarming 

 in them. In this animal interstitial cells must have been present 

 in the tentacles, which is not usually the case. 



The period from the freeing of the egg to the hatching of the 

 young Hydra varies with the season. A batch of eggs set 

 free in November hatched in January, while some produced 

 in summer took only about three weeks to develop. In many 

 cases the eggs failed to hatch owing to the attacks of bacteria 

 or fungi. The young Hydra emerges by a crack in the shell, 

 usually equatorial. It is oval and almost colourless, but in 



