324 MR FRANK BALFOUR-BROWNE ON 



I am not sure as to when the males reach maturity, but they are sexually excited 

 early in February. Possibly the females are " fertilised " in the autumn, as, so far as I 

 have observed, they will not take a male at the beginning of the season. The only time 

 I have seen them accept a male is immediately after having completed an egg- cocoon. 

 Donisthorpe (I.e., p. 291.) refers to the refusal of the female Hydrophilus to accept a 

 male as a case of sexual selection. So far as my experience goes, it is not a question of 

 the choice of a male by the female, but of the male courting the female at the wrong 

 time, and if a female has her spermotheca full of spermatozoa, she wi]l not unnaturally 

 reject any male. Immediately after completing an egg-cocoon a Hydrobius will accept 

 any male which offers, and I expect the same is the case with Hydrophilus. 



The courtship is a somewhat strange phenomenon, and it is the only period at which 

 I have heard the male stridulate. I think that the males are only excited during the 

 daytime, at least in the earlier months of the year, and require suitable light and 

 warmth to arouse them. For instance, in February or early March in my aquaria, kept 

 in a warm room, there are few beetles visible at 9 a.m., most of them being amongst 

 the stones at the bottom. About 11 or 11.30 the sun reaches the aquaria, and then 

 all the beetles come to the surface and move about rapidly and feed and the males are 

 then excited. If at 9 a.m. the temperature of the water is raised from 50° F. to about 

 60°, the same phenomena are observed as occur later in the morning under the 

 influence of the sunshine. 



The male sits on the back of the female rather in the position of a jockey on a race- 

 horse, that is, well forward, his metasternum being about over her prothorax. His 

 head is bent right over hers, and his courtship consists in drumming upon her labium 

 with his maxillary and labial palpi. His maxillary palpi pass round outside the bases 

 of hers. She bends her head downward as if trying to avoid his attentions, and her 

 maxillary pa]pi wave about. Her jaws can be seen working, and she occasionally 

 succeeds in biting the palpi of the male. The front tarsal claws of the male hold on 

 either in front of the eyes or behind them or even to the eyes themselves ; the mid- 

 tarsal claws catch the posterior margin of the female prothorax, while the posterior tarsal 

 claws hold the borders of the elytra. 



If the female is very annoyed by the attentions of the male she signifies it by 

 swaying rapidly from side to side, or by running quickly over the submerged vegetation, 

 and, as a rule, after a short struggle the male desists. Otherwise she may feed quietly, 

 quite regardless of his wooing. He makes occasional attempts at copulation by rapidly 

 moving backwards and extending his abdominal segments and the penis, but the 

 female usually sweeps the latter away with her posterior tarsi. After making several 

 ineffectual attempts the male usually desists and goes in search of another mate. 



During courtship the male keeps up a faint but distinct stridulation, reminding one 

 of a corncrake at a great distance. At the moment the noise is produced the ventral 

 side of the abdomen collapses like bellows, as if expressing air, and at each collapse of the 

 abdomen the apex bends downwards. I can find no stridulating file. The noise is not 



