352 DR. N. ANNANDALE ON 



It may further be pointed out that in Protohydra and Microhydra, forms which there 

 is good reason to regard as degenerate and not as primitive, sexual reproduction is not 

 known to occur. 



Development of the Egg — 



The eggs generally adhere to the parent until the latter dies. Before dying it re- 

 tracts its tentacles and sinks to the bottom. If three eggs are produced, however, the 

 first may fall off and sink independently before the parent becomes moribund. 



I have not been able to rear eggs in my aquarium. Thick-shelled eggs lay at the 

 bottom for some weeks and then broke up ; while thin-shelled eggs degenerated within a 

 few days of their production. The ectoderm cells parted from one another and ruptured 

 the envelope of the egg. They then became amoeboid and moved slowly in different 

 directions for some hours before dying. The endoderm cells, only a few of which were 

 present, assumed a spherical form, remained stationary, and perished rather more 

 rapidly. Their contents were more homogeneous and transparent than those of the ecto- 

 derm cells. 



Duration of Life. 



The duration of life of Hydra orientalis is evidently short. In captivity indivi- 

 duals rarely live for more than a few weeks, while in the natural environment there 

 is evidence that they do not survive for many months. In the cold season of 1905-06 

 most specimens found in the middle of November were extremely small, with only 

 four tentacles. A fortnight later all but a few had grown two additional tentacles, 

 had increased greatly in size, and were producing buds. The hot weather which com- 

 menced at the beginning of the last week in December, killed most or all of these 

 parent individuals, only smaller and attenuated examples, which had recently been 

 buds, remaining in the "tank." Most of these had five tentacles when set free, the 

 others having six. A few weeks later it was quite exceptional to find a budding 

 individual with only five tentacles. This brood also perished shortly, for the indi- 

 viduals found in the latter half of March and in April had, in a large proportion of 

 cases, five tentacles only ; while those found in May and June were generally devoid of 

 buds and as a rule had four tentacles, closely resembling individuals taken in the pre- 

 vious November. These observations refer to a single pond. It is therefore probable 

 that under the most favourable conditions an individual of the species may 

 live for several months, but that a few weeks is not uncommonly the period of life. 

 If this be so, the short life of the individual is another instance of the low vitality of the 

 Bengal form as compared with its European congeners, which have been known to live 

 for as long as two years in captivity. The evidence regarding the Bengal species, 

 however, refers only to Calcutta. 



Favourable and Unfavourable Conditions. 

 It may be well to point out briefly the conditions which appear to be favourable 

 or unfavourable to the occurrence, growth and survival of the species in its natural 

 surroundings. In the town of Calcutta I have only found the polyp very abundant in 



