REPRODUCTION OF ASELLUS AQUATICUS. 339 



will be obvious that the association is of real value. The chnnce of male 

 and female not meeting at the right time, and the fact that in all probability 

 the female would be in hiding, makes this marriage-clasp most important. 



When the ecdysis is about to take place, the male gives his attention to 

 the female, and seems to assist her in working oft' the hind-half by walking 

 slowly forwards a few steps and by holding her in such a position that the 

 waving motion can be performed with ease. When the cuticle is oast, the 

 female is ready for the attentions of the male. He need not wait until the 

 fore-part is cast, for the oviducal openings are on the 5th thoracic segment, 

 and this segment is exposed by the casting of the hind-half. The male now 

 adjusts the position of the female so that her 5th thoracic segment is 

 immediately below his 2nd pleopod. Kaulbersz mentions that the impreg- 

 nation takes place with the creatures belly to belly. I have never seen this. 

 All that I could see of this operation was a sideways sliding of the body of 

 the male, so that the ventral surface of his body pressed against the side of 

 the female's thorax. It looked almost like a hugging of the female, and the 

 arrangement would certainly bring the 2nd abdominal appendages into the 

 immediate neighbourhood of the female reproductive openings. After 

 occupying this position for some time on one side, he changed sides and 

 the operation was repeated. I have kept couples under observation during 

 the whole of this period, that is to say from the casting of the hind-half to 

 the release of the female, and have never seen the two individuals with 

 ventral surfaces opposed. The length of this active copulation period varies 

 somewhat. In one case it only lasted an hour. The hind-half of the 

 female's cuticle was finally cast free at 8.30 p.m. after two hours beino- spent 

 on this operation. The male waited about 20 minutes before beeinnino- 

 copulation, and this was completed and the female released by 9.30 p.m. 

 This was the shortest time recorded, the average being from 2 to 3 hours. 

 In one case it lasted 5 hours. 



After separation from the male, the females had a mass of spermatozoa in 

 the expanded receptacles just within the openings on the 5th thoracic 

 segment. I have verified this bv dissection and by paraffin sections (PI. 26. 

 fig. 12). 



The female is now released, as the purpose of her long association with the 

 male has been achieved ; and she seeks some convenient hiding-place, under 

 a leaf or stone or in a hollow stem, to await the completion of her ecdysis, 

 and with it the release of the oostegites. This completion of the ecdysis 

 takes place usually about 24 hours after the first part, but 1 have a record of 

 8 hours only. 



The oostegites are now released. Up to this they have been represented 

 by small club-like processes; but if one of these is examined, the much 

 larger plate-like oostegite is seen folded up within, like a leaf in a bud waiting 



