g G. C. Embody. 



2. Mating. 



Prof. S. J. Holmes gives a very excellent account of the mating 

 of Hyalella dentata. He concludes that as the sexual impulse appears, 

 the males find the females accidentally; that neither sight nor the ol- 

 factory sense play any part in the process. Briefly stated, the male 

 comes in contact with the female which immediately curls up the ab- 

 domen and remains impassive. The male grasps her with his gnatho- 

 pods and after much jerking finally adjusts his companion to the proper 

 position and swims about through the water bumping into various ob- 

 stacles. Throughout the mated period the female remains unresisting, 

 simply grasping whatever food may come within reach and constantly 

 moving her pleopods to aerate the gills. 



Miss Smallwood observed (1905) that in Orchestia palustris, 

 the male hooks the dactylus of the large gnathopod under the anterior 

 edge of the fourth or fifth coxal plate on either side, right claw used 

 mostly. The bases of the peraeopods and the flexed abdomen assisted. 



2d .7? Qnoih. 



ZdHt...., 



Fig. 1 — 3. Position of gnathopods during mating. 



A number of mated individuals of Gammarus limnaeus were 

 placed under observation during February and March, 1910. There 

 was found to be some variation in the manner in which the males 

 grasp the females. A very secure hold and one commonly used was 

 as follows; dactylus of first left gnathopod hooked caudad into the 

 suture between the head and the first dorsal plate, the dactylus of the 

 second right gnathopod hooked cephalad between the fourth and fifth 

 dorsal plates (fig. 1) the other gnathopods remaining free. The peraeopods 

 and flexed abdomen may have assisted but their use seemed not to 



influenced by tiie external heat. It is therefore quite safe to take the mean tempe- 

 rature as representing the average condition of the water during the reproductive 

 period. 



