NOTES ON THE LIFE HISTORY OF GAMMARUS CHEVREUXI. 547 



surroundings, with stones, and plenty of mud and dirt provided for the 

 shelter the animals seek when they moult, etc. Our method of work, 

 however, necessitated daily observations being taken without unneces- 

 sary disturbance, and the bowls had therefore to be kept in the light, 

 free from dirt and dust, and with only just sufficient ulva for food and 

 not enough to provide a hiding-place. 



We chose for our experiments the brackish-water Oammarus 

 chevreuxi, as being easily obtainable in the neighbourhood. It occurs 

 in the ditches draining Chelson Meadow (see previous paper). 



GENERAL METHODS. 



We brought our first specimens to the Laboratory on June 4 of last 

 year (1912), together with some of the water, ulva, and the isopod 

 Sphaeroma served um, from the same ditch. 



The next day two mated pairs were taken, and daily observations 

 commenced. We kept these in jars partly covered to exclude dust, 

 but a sufficient supply of air was ensured by a continuous bubbling of 

 air through the water. We have found since that this is not essential, 

 provided enough air can be supplied in some other way, such, for 

 instance, as exposing a large surface of water to the air. In this way 

 several broods have done well in large crystallizing dishes, abont 

 twelve inches across and two-thirds full of water, dust being excluded 

 as in the jars. We consider, however, that we get better results, with 

 the older animals at any rate, when the water is aerated. 



With regard to the young, experience has shown us that the best 

 method of observing them through their various stages to sexual 

 maturity, and of obtaining their moults as they are cast, is to place 

 each individual in a separate finger-bowl, half full of water, and almost 

 wholly covered with a glass plate. The water is aerated once a day 

 with a pipette, and a little ulva is given for food. 



All the dishes and jars have been kept in ordinary diffused daylight, 

 not protected in any way. 



The temperature in the Laboratory in summer probably does not 

 differ much from that in the ditches, but in winter it is considerably 

 higher. It varies through a number of degrees at different times of 

 the day and on different days. The animals, however, appear but little 

 aflected by this variation. The only point we have noticed is that 

 the rate of development and the time of reaching sexual maturity are 

 retarded by a lower temperature. In the Laboratory from October to 

 December the temperature of the water in the moult-bowls varied 

 between 10°-16° C. ; in another room not artificially heated the range 



