NOTES ON THE LIFE HISTORY OF GAMMARUS CHEVREUXI. 549 



located, but we feel certain that in our species the animals always 

 employ the antennae in meeting others, and in recognizing their own 

 species. 



Sexual maturity in both sexes is attained when the animals are 

 about half grown. The time they take in reaching maturity varies 

 greatly, but the cause of such variation is not yet known. The young 

 produced in summer appear to become mature in much less time than 

 those hatched later, but this cannot be laid down as a rule, as there 

 is evidently some other potent factor at work besides temperature. 

 The first brood of Pair I was extruded on June 19th and reached 

 maturity on July 25th, i.e. in thirty-six days. Sometimes, however, a 

 later brood will reach maturity before an earlier ; for instance, Brood 

 II of Pair II, extruded July 4th, did not reach maturity till September 

 4th, a period of sixty-two days, while Brood IV of the same pair, 

 extruded July 29th, became mature on September 9th, only forty-two 

 days. 



The male takes the female when their respective gonads are becom- 

 ing mature and carries her sometimes for days before mating takes 

 place. This occurs once a fortnight with the female, so that, in ideal 

 conditions, twenty-six broods could be produced annually. This 

 would imply that breeding continues throughout the year, and such 

 we believe to be the case, at any rate in a mild climate like Plymouth. 

 It has gone on uninterruptedly in our jars during the seven months 

 we have been working, from early in June to mid-January, and breeding 

 pairs are still found in the ditches in Chelson Meadow. 



The male, on the other hand, seems to have no regular mating period, 

 but can fertilize a succession of females with an occasional period of 

 rest. One young male, which became sexually mature on September 

 28th at the age of fifty-two days, by October 1st had fertilized the 

 three females in the same jar. An interesting point to note is that 

 the last female had only two eggs, and these were thrown off the next 

 day, which may have been due to the fact that the eggs were not 

 properly fertilized, and also suggests that the number of eggs 

 extruded may bear some relation to the condition of the male. Again, 

 in Brood I of Pair I a male and a female became mature in thirty-six 

 days ; four days later four other females were fertilized by this male 

 and another, and again the last females mated had a small number of 

 eggs, five and seven respectively, while the first female had eighteen. 

 How many times in succession a male can mate we do not yet know, 

 because we have never had a succession of females in the right 

 condition. If a male is placed in a dish with several females whose 

 eggs are at diM'erent stages of development, he chooses one with advanced 



