T.\(.GART] CRAYFISH STLDV 107 



abdomen. A strange habit exhibited at this period, a rhythmic 

 lying d©\vn and rolHng over, is not to be interpreted as sickness, 

 but as a necessary part of the complex series of phenomena con- 

 cerned in the fertilization of the eggs and in their firm fixture to 

 the abdominal appendages of the female. To insure the fertili- 

 zation and future development of all the eggs it is well to leave 

 the female undisturbed for a couple of days till the mucus is gone 

 and the eggs firmly fastened, each by its own strong stalk. 



"From that time on for a term of five to eight weeks, which, 

 according to the temperature, will be necessary to bring the eggs 

 to the hatching period, the crayfish may be lifted out of the water 

 whenever desired and a few eggs removed for closer observation." 



The teacher's knowledge of the morphology- of the crayfish 

 can be increased, of course, by any textbook in zoology. The two 

 sexes are easily distinguished by the greatly modified first 

 abdominal appendages in the male and the annulits zcntralis, the 

 rounded structure between the last pair of walking legs, on the 

 female. For anyone who cares to compare the diflterent species, 

 the shape of the first abdominal appendages of the male are the 

 most constant characters, although the shape of the rostrum and 

 of the claws are of value. A number of times when collecting 

 I have made the acquaintance of small boys, who were most in- 

 terested in learning that crayfish had names and could be iden- 

 tified. One day two boys who happened along sorted eighty 

 crayfish into three different species without a mistake after I had 

 explained the distinctive characters of each. 



Problems. 



1. Digging out a crayfish burrow is an interesting bit of 

 work for energetic boys. The burrows vary greatly in size, 

 depth and shape, and it makes a nice little problem deciding on 

 the factors which determine the matter — such as depth of ground 

 water, size and number of crayfish, kind of soil, etc. Observa- 

 tions may be made on the chimneys if they are at all plentiful. 

 It is not uncommon to find quantities of them, commonly called 

 "snake holes,** on a bit of lowland. 



2. It is a matter of dispute among investigators whether the 

 chimney is a necessary and invariable part of the burrow, whether 

 (if it be closed at the top) it is closed on purpose or accidentally, 

 and how many crayfish occupy a burrow. 



3. If field work can be done it is possible to work out the 

 most eflfective way of catching crayfish. Since the animal when 

 disturbed usually jumps backward and upward by a violent flex- 



