g G. C. Embody. 



show that one amphipod will kill and devour its neighbor. In certain 

 aquaria where pairs had been isolatod, the female mysteriously disap- 

 peared, usually immediately after moulting. In one aquarium two 

 different females disappeared in one week, only the exoskeletons being 

 left. A third female was admitted and a day later the male moulted 

 and died. The female continued to live in this same aquarium through 

 five different moults. 



V. Reproduction. 



1. Period. 



Collections representing the three species, Hyalella knicker- 

 bockeri, Eucrangonyx gracilis and Gammarus fasciatus, were 

 taken from Ithaca waters almost weekly from October, 1908, until 

 August, 1910, except during the colder periods of winter when Cayuga 

 Lake and tributaries were frozen. Individuals of Gammarus limnaeus 

 and also E. gracilis Avere collected from a trout brook near Auburn, 

 New York upon the following dates: Jan. 8 and 22. April 5, July 10, 

 1909; Jan. 22 and Sept. 10, 1910. 



In the following table II, are given the earliest and latest dates 

 upon which the various species were found breeding, together with 

 the approximate length of the total reproductive period of each spe- 

 cies ^). 



Table E. 



^) The reproductive period as given for the species must not be confused with 

 that for the individual. The two may or may not be identical. That they are iden- 

 tical is indicated by the fact that in almost every collection the breeding females 

 were in the majority over non-breeding ones. On the other hand the pairs under 

 observation in balanced aquaria indicated that the individual's reproductive period 

 was of comparatively short duration, for not. a single female produced more than 

 throe censecutive sets of eggs and these within a period not to exceed sixty days. 



*) If the trout brook near Auburn, New York, were to be studied during the 

 months of October, November and December, the reproductive periods of E. gracilis 

 and G. limnaeus might be showed to be longer. 



*) Since young were found in the brood pouches of many females on this date 

 and since the period of incubation (p. 13) is 21 days or undoubtedly longer at lower 

 temperatures, it is very probable that the reproductive period is twenty one days or 

 more, longer than is indicated by the date here given; hence the approximate period 

 is used as corrected from 245 to 266 days. 



