THE COMMON HYDRA OF BENG-AL. 351 



fresh to have a rough surface of a yellowish colour ; but its external characters are con- 

 cealed after a short time by the minute particles of extraneous debris which are retained 

 by the spines on its surface. These spines cover the whole surface except a small, 

 flattened, subcircular area at the point at which the egg is in contact with the mother 

 polyp. This area is naked and almost smooth. 



Should the egg be thin-shelled, it is covered, when the external membrane ruptures, 

 merely by a smooth, semi-transparent membrane, which is to a certain extent elastic. 

 At first there are a couple of ridges on its distal pole which are parallel to the main 

 axis of the polyp and look like the tumid lips of an opening ; but I have not been able 

 to detect any aperture. As the embryo increases in bulk, the ridges disappear on 

 account of internal pressure, and only a single, small, simple, knob-like projection 

 remains, its position marking the pole furthest from the point of emergence of the 

 ovum. It is clear that eggs of this kind lack the thick horny shell which the cells of the 

 ectoderm usually secrete in the young embryo of Hydra. So far as my investigations 

 go, they differ in no other respect from normal eggs. 



Thin-shelled eggs are produced either after the production of one or more thick- 

 shelled eggs or by unusually small parents which have only a single ovary. I have 

 known a case in which one thin-shelled and two thick-shelled eggs were attached to the 

 same individual at the same time. It would therefore appear that the degenerate 

 condition of the thin-shelled egg is due to exhaustion on the part of the parent. In this 

 connection it is perhaps worth emphasizing the fact that the eggs are produced with 

 greater rapidity than are the spermatozoa. No surprise need be caused by the pro- 

 duction of degenerate eggs if we consider that during the course of a year not a 

 single individual was found which bore eggs at all, under natural conditions. I am 

 inclined to believe that sexual reproduction plays a very unimportant part in the life 

 cycle of Hydra orientalis, and that when it occurs it is almost a pathological pheno- 

 menon. I was formerly led to take a very different view, viz., that large numbers 

 of eggs were produced in spring and lay dormant during the hot weather, the adults 

 invariably perishing about the end of March. But the discovery that budding, after 

 becoming temporarily less common in March, again becomes more common in April, 

 that buds produced late in the season have often only four tentacles, and that polyps are 

 found occasionally during summer,appears to agree with the ascertained facts that few in- 

 dividuals bearing eggs are found in a state of nature and that no such individuals have 

 been seen at any season except the beginning of spring. The production of spermatozoa 

 does not call for the same expenditure of reserve material as does that of eggs, and it 

 must therefore be expected that the organism will be more liable to return to the ances- 

 tral condition as regards the production of the former than as regards that of the latter. 

 The vast majority of the sperms produced by most animals perish without fertilizing 

 ova, and it is by no means impossible that the males of Hydra orientalis are practically 

 instances of atavism, parallel to rarer instances of the same phenomenon in the case of 

 females in the same species ; in other words, that a local race of Hydra has been pro- 

 duced from ancestors in whose life cycle sexual reproduction played an important part, 

 and that in this race budding has become the normal method of continuing the species. 



