Andrews] THE KEEPING AND REARING OF CRAYFISH 299 



such a female will predict the time it is going to lay by a most note- 

 worthy process of cleansing that goes on several clays before the eggs 

 are laid and which should be carefully studied as a purposeful 

 instinct. 



The female about to lay should, preferably, be kept little disturbed 

 and with one corner of the dish screened to give shade. 



The actual laying will, with rare exceptions, take place in the night 

 and the next morning the pupils may dimly see some hundred of eggs 

 held enclosed in a mass of mucus under the abdomen. A strange 

 habit exhibited at this period, a rythmic lying down and rolling over, 

 is not to be interpreted as a sickness but as a necessary part of the 

 complex series of phenomena concerned in the fertilization of the eggs 

 and in their firm fixture to the abdominal appendages of the female. 

 To insure the fertilization 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 accord- 

 ing to the temperature, will be necessary to bring the eggs to the hatch- 

 ing period, the crayfish may be lifted out of the water whenever de- 

 sired and a few eggs removed for closer observation. 



In this long time the pupils should look for evidences of maternal 

 care in the treatment of the eggs. 



It is evident that any class meeting in April and May may expect 

 some material to show stages in the development of the eggs and as 

 each female lays from three hundred to six hundred eggs it is easy to 

 have an adequate supply. In watch-glasses and strong light even a 

 pocket-lens reveals stages in cleavage and shows many of the forms 

 of embryos figured by Reichenbach, by Huxley, and in text-books of 

 zoology and embryology. With a compound microscope available 

 for demonstrations, the brilliance of the pigment, the beat of the heart 

 and the flow of the blood, in fact the livingness of the embryo within 

 its shell are most fascinating and give the students hope that the long 

 expected hatching will take place; and it will after about two more 

 weeks. 



With time, skill and apparatus the teacher could utilize the mate- 

 rial presented for unlimited illustrations of the mere special facts of 

 crustacean embryology; if that were advisable. The first week of 

 incubation would supply eggs in cleavage stages, the second the 

 beginning of the embryo, the third the "nauplius stage," the fourth 



