THE COMMON HYDRA OF BENGAL. 347 



position of the gonads and by the four tentacles of the spring and autumn bud, is 

 given of something like a primitive four-rayed symmetry, which may possibly be masked 

 by complications due to more vigorous metabolism in other species. It may be pointed 

 out that four is a common number of tentacles for young individuals ' of other species 

 of the genus to possess, but the number does not appear to be quite constant in any 

 form. Brooks 2 and others have called attention to the existence of bilateral symmetry 

 in certain Hydroids (e.g., in the larvae of Cunina octonaria and in Eutima miva) and 

 it is not impossible that the four-rayed symmetry of this Oriental polyp may repre- 

 sent a stage in the production of a symmetry which seems superficially more simple. 



(3) Sexual Reproduction — 



I have already stated that Hydra orientalis is dioecious, and this will be a con- 

 venient point at which to give the evidence on which I rely in regarding those indi- 

 viduals which produce spermatozoa as distinct from those which produce eggs. In the 

 first place, if a large number of individuals are kept together in captivity, a proportion 

 (approximately one half) of them develop male gonads, unless they all die shortly after 

 capture. The remainder either bear eggs or die before showing any signs of sexual 

 activity. The males continue to produce spermatozoa for a period varying from a few 

 days to a fortnight of rather more, and then die. The females die after producing one, 

 two, or three eggs, their life after they have reached sexual maturity being limited to a 

 period of a week or less. I have not known eggs to be produced in cold weather ; but 

 spermatozoa have been produced by males living in unnatural conditions in my 

 aquarium even during normal winter weather. I have failed to keep a male alive 

 even until the contents of all its spermaries have been discharged. 



The following experiment would suggest that individuals assume one sex or 

 the other at a very early stage. Four small, colourless polyps, each with four 

 tentacles, were placed, in the middle of November, in a small, narrow glass jar contain- 

 ing clear tap water in which a few Cladocera had been liberated. The jar was kept in 

 a room with closed shutters, which not only kept out the light but rendered the air 

 extremely close. Certain other animals (e.g. mosquito larvae) kept under the same 

 conditions did not survive for a single night ; but the Cladocera continued active. Of 

 the four polyps none produced an additional tentacle, increased in size, became 

 darker in colour, nor attempted to feed ; but one of them, after ten days, commenced 

 to develop certain outgrowths, which a microscopical examination proved to be 

 immature spermaries. Before they became ripe it died. The remaining three polyps 

 lived for some weeks without apparent change, and then died also. In every case in 

 which I have attempted to repeat this experiment, or to ascertain the effect of starva- 

 tion on the polyps, my ' material ' ' has perished, without producing either buds or 

 gonads. 



In spite of the evidence given above as to the distinction of the sexes in the species 

 (which evidence is mainly negative), it is possible that hermaphrodite individuals may 



1 See Kleinenberg's Hydra, p. jH, pi. HI, fig. 14, 2 Zoul. Anz,< VII, 1884, p- 710. 



