298 THE NA TU RE- STUD Y RE I VE IV [ 2 : 9 _ DE c., .906 



At the best every crayfish is not always hungry and removal of 

 excess of food and change of diet seem here, as elsewhere amongst 

 animals, to increase the chances of long life. With running water 

 and a varied diet crayfish have been kept alive and breeding for 

 three years in small sinks in this laboratory. 



Yet mortality from unknown diseases may occur and after the breed- 

 ing season many males may die, and, eventually, a limit to their life 

 seems reached in a few years, judging from experiments made by 

 the writer. 



While the crayfish is so well known and extensively used for 

 anatomical and morphological study, it is also a most excellent subject 

 for study of comparative psychology and of animal behavior. More 

 than that, it is, we find, unusually well fitted to show students scenes 

 in an entire life-history of an animal large enough, common enough 

 and complex enough to interest all pupils and at the same time not 

 too much like a human being. Any school that has running water 

 and six square feet of sink space to devote to this purpose may hope 

 to present to the pupils in three months the fundamental facts of sex 

 and of egg laying and development, of maternal instincts and of larval 

 life; while within a year the whole cycle from egg hatching to egg 

 laying again may be watched in the same animal. 



The following method of rearing crayfish apply strictly to C. affinis 

 which lays its eggs in the spring; some other species have other 

 breeding seasons and less ability to endure the artificial conditions of 

 captivity. Specimens of C. affinis are shipped in large numbers to 

 the New York markets and they may be obtained directly from Mr. 

 L. Davis, Accokeek, Md., at prices varying from one to five cents 

 each according to the season and number purchased. 



If the crayfish are obtained in the autumn or in the winter the 

 sexes may be keep together till about the middle of March, unless it 

 be thought desirable to study the remarkable and instructive mating 

 habits. In that case a male should be kept in a small dish till accus- 

 tomed to it and then a female of like size introduced whenever the 

 process of pairing is to be observed. If properly understood these 

 phenomena have too deep an educational value to be left out of the 

 study of the whole life cycle. 



In March the females may be put into dishes of running water by 

 themselves, one, or but few, in each dish. The indication that 

 a female Cambarus is likely to lay eggs is that the annulus ven- 

 tralis shows a white speck, or plug, projecting from its orifice. And 



