32 G. C. Embody. 



2. E. gracilis and Hyalella have the widest distribution. They thrive 

 in waters varying widely in temperature, from warm, partially stagnant, 

 marshy pools to the cold, running waters of the trout brook. G. fasciatus 

 seemed to be restricted to Cayuga Lake and its more open tributaries. 

 G. limnaeus is confined to the cold trout brook. 



3. All forms were always found associated with vegetation, either living 

 or dead (leaves). 



4. The food of the four species is essentially the same and consists of 

 Uving or dead animals and plants. The former must not be too greatly de- 

 composed. The exuding Juices from a freshly killed Asellus seem to attract 

 while those from a Planaria seem to repel amphipods. 



5. Hyalellas were found breeding throughout a period of 152 days 

 during a year; E. gracilis, 299 days; G. fasciatus, 199 days, and G. 

 limnaeus 266 days. 



6. G. limnaeus ceased breeding in aquarium water when the tempera- 

 ture of the latter approached 18 C. The other three species will breed when 

 the temperature is as high as 30 C. 



7. The males of G. limnaeus, G. fasciatus and Hyalella may mate 

 with females even when the latter carry eggs or young in the brood pouches. 

 According to the writer's observations the males separate permanently from 

 their mates immediately after semination. 



8. The average number of eggs deposited at one time by a female G. 

 limnaeus is 25; G. fasciatus, 22; E. gracilis, 45; Hyalella, 18. 



9. The period of incubation varies inversely as the temperature of the 

 water but not in a constant ratio. It is quite probable that all eggs of G. 

 limnaeus hatch in not less than 18 days after oviposition. 



10. The young of E. gracilis when first hatched are smaller and noti- 

 cably weaker than those of G. limnaeus. 



11. The young amphipods remain in the brood pouch during a period 

 varying from 1 to 8 days; but during this time the young of E. gracilis 

 at least, may have left temporarily and voluntarily reentered the pouch 

 several times. 



12. The recurrence of oviposition follows closely the recurrence of 

 ecdysis. 



13. The period between moults in the case of young amphipods is much 

 shorter than that in the case of adults. 



14. In general the period between moults in the case of adults increases 

 as the average mean daily temperature decreases. 



15. The young of E. gracilis grow slowly as compared with those of 

 the other three species; probably not reaching sexual maturity until the second 

 year. The young of the other three species mature and reproduce many times 

 during the first year. 



16. G. fasciatus has the greatest reproductive capacity followed in 

 order by Hyalella, G. limnaeus and E. gracilis. 



17. The important enemies are found among the birds, fishes and insects. 

 Hydras may destroy the young of E. gracilis in considerable numbers. 



