NOTES ON THE LIFE HISTORY OF GAMMARUS GHEVKEUXl. 5oo 



Another brood kept in the Laboratory gives a record of four moults 

 in twenty-eight days. As contrasted with the two broods tabulated 

 above, the period between the moults was much less, due no doubt 

 to the higher temperature. Another instance is the " control brood " 

 for Brood II, which was kept in the warm Laboratory ; they were one 

 day ahead of Brood II in the first moult and seven days ahead at the 

 second moult. 



EXPEKIMENTS IN VAEYING THE SALINITY. 



Great variations in the salinity of the water can be endured by this 

 species, but too sudden a change tries them severely. We have made 

 some experiments with large adults. In one instance a male and 

 a female were taken from the brackish water and put into fresh water 

 on July 24th ; two days later the female died, the male survived till 

 the seventh day. Again, on July 24th, a male carrying a female was 

 put into sea-water ; they both moulted, and five days later were 

 separate, but no eggs were produced. On August 3rd the male was 

 again carrying the female, and on the 7th she moulted again, and 

 again they were separate and no eggs present. On August 21st they 

 were again paired, and on the 24th another moult was found, and the 

 female was dead. The male died on the 26th, so he had lived thirty- 

 three days and she thirty-one. Evidently the sexual impulse was still 

 there, but the power to produce was affected. In a third case, two half- 

 grown females were put straight into sea-water. One had very young 

 eggs, which were soon thrown off; the other had two partly hatched 

 eggs, which hatched and were extruded four days later. The two 

 females are still alive, a month later, and their ovaries are much 

 enlarged. The extruded young are swimming about in the sea-water. 



Similar experiments just commenced with newly hatched broods 

 promise some interesting results. They show that the first moult is criti- 

 cal ; if that be survived they continue to flourish, but the period between 

 moults is much longer than normal. One brood of seven G. chevreuxi 

 were put into fresh water ; they took from eighteen to twenty-one days 

 to reach the first moult, and all died, either in moulting or directly after. 

 Some nine G. pulex put straight into brackish water all accomplished 

 their first moult safely, but took thirteen to fifteen days instead of 

 seven to reach it ; nine others of the same brood put into water one- 

 third brackish to two-thirds fresh took nine days to this moult. 



Finding the sudden change too drastic, a number varying in size 

 were put on September 9th into two bell-jars. Small quantities of 

 fresh water have been added to the one from time to time at a few 



