199] REGENERATION OF CRAYFISH APPENDAGES II 



placed in a pond, as there the conditions were as nearly normal 

 as possible. This method proved unsatisfactory, however, for 

 even when the cage was left undisturbed by intruders, as was 

 not always the case, I had no means of keeping a record of in- 

 dividual crayfish. Keeping them in standing water in the labo- 

 ratory was attended by one especially objectionable result. A 

 sediment, and in some cases, a fungus growth, appeared all over 

 the animals. I tried various means of removing this, which was 

 particularly troublesome about the eyes, the antennae and the 

 bases ofi the legs, but the only practicable method was to give 

 them occasionally a thorough scrubbing with a rather stiff brush. 

 Care has to be taken not to break ofif their legs in this operation. 

 It was practically impossible to keep them in running water, as 

 individual crayfish had to be placed in separate dishes. But the 

 presence of sand or gravel in the vessels seemed to make condi- 

 tions a little better, although it increased the difficulty of feed- 

 ing the crayfish. 



As was mentioned above, I at first tried feeding them every 

 day, but at last learned that they thrived much better if fed only 

 once or twice a week. 



The method I now use is to keep each one in a separate 

 glass dish, with or without gravel in the bottom; nearly cover 

 them with water, changing it every other day, sometimes every 

 day ; feed them once or twice a week with fresh meat, occasion- 

 ally with bread. They are especially fond of fresh liver and of 

 crayfish flesh. The method is not altogether satisfactory, but it 

 yields a fair degree of success. 



I further found that the success of an experiment also de- 

 pended greatly upon the time of year at which the crayfish were 

 operated upon. Those operated upon during the fall and winter 

 seldom live through a moult and often do not moult at the 

 usual season. Apparently their inactivity in the laboratory is 

 not conducive to good health, and since the moult probably does 



