Distribution, Food and reproductive Capacity of some fresh-water Amphipods. 15 



Miss Smallwood indicates (1905) that the young of Orchestia 

 palustris voluntarily leave the brood sac from three to four days after 

 hatching. Some individuals which were forcibly taken from the brood 

 sac gradually reentered it. 



On May 24, 1909, a pair of E. gracilis were isolated in a dish 

 of water containing aquatic plants. The female contained eggs which 

 hatched two days later. On the twenty eighth, one young had left 

 the pouch and was found swimming about. On May 20, six young 

 were found either swimming about or feeding among the plants. Two 

 hours later these six could not be found. Upon gently tapping the 

 mother, four young left the pouch and swam about until one by one 

 they collided with their parent, clung to the hair-Uke processes from 

 the lamellae forming the brood pouch and finally wedged themselves 

 into the pouch. On June first one young voluntarily issued from the 

 brood pouch, swam to a piece of Spahagnum, secured a good meal 

 from the same and then began to swim aimlessly about the dish. In 

 time it came in contact with its parent and immediately reentered her 

 pouch. 



A like behavior of other individuals of the same brood was noted 

 on each succeeding day until June 5 th., when all young had left the 

 pouch and none were observed to reenter. The observations point to 

 an instinct analogous to that which Andrews has shown (1907) to be 

 highly developed in the young of the second and third larval stages 

 of Astacus leniusculus and Cambarus affinis respectively. None of 

 the young of Hyalella or G. f asciatus was observed to re-enter the 

 brood pouch after once having left it. The activities of the young of 

 these species, however, were not followed closely and this particular 

 habit may have escaped observation. 



In the following table VI is given a summary of the data indi- 

 cating the length of time the young of each of the four species remain 

 in the brood pouch. 



It was observed in the case of Hyalella, G. limnaeus and 

 G. fasciatus that the exit ef the young might be hastened in two 

 ways. 1. The females usually mate a second time before the young 

 of the first broods have left the pouches. The struggle of the 

 males in such cases usually forces the exit of the young. 2. The 

 females occasionally moult prematurely, when the young are gotten 

 rid of with the cast skins. In such cases the young were never obser- 

 ved to re-enter the pouches of the Uving females but were often found 

 in the cast skins. 



