No. 545] THE BIOLOGY OF THE CRAYFISH 281 



one end, and the other a still water aquarium arranged 

 to furnish a more nearly natural habitat. 



In this paper I have not touched upon the anatomy or 

 the work on regeneration, but have confined myself to 

 what is generally known as ecology or biology. In the 

 attempt to make the paper fairly complete I have referred 

 in the text to the numbers in the bibliography. 



It is a pleasure to acknowledge my indebtedness to Dr. 

 C. F. Hodge, Dr. Newton Miller and Dr. J. P. Porter, of 

 Clark University, Dr. A. E. Ortmann, of the Carnegie 

 Museum of Pittsburgh, and Dr. E. A. Andrews, of Johns 

 Hopkins University. 



Senses 



Touch.— Touch is probably the sense of greatest value 

 to the crayfish. It is sensitive to touch over the whole 

 surface of the body (16), especially on the chelae and 

 chelipeds, mouth parts, the ventral surface of the abdomen 

 and the edge of the telson. 



Vision.— The crayfish, in common with the insects, has 

 a compound eye. It is believed by many that the com- 

 pound eye is a visual apparatus which is almost worthless 

 for detecting the forms of objects, especially if these 

 objects are stationary; but that it may furnish a very defi- 

 nite response to stimuli of moving objects. 



Bell's experiments with the crayfish (16) showed that 

 there was no response to stationary objects. The case was 

 entirely different with large, moving objects. The 

 response was not due to any change in the intensity of 

 light such as that caused by a shadow falling on the ani- 

 mals, for they would react to a movement made on the 

 opposite side of them from the window. Reaction to 

 smaller moving objects was not so marked. 



Crayfish are sensitive to strong light and hide during 

 the day under stones, among roots of plants near the bank, 

 and in burrows in the bank. It is a noteworthy fact that, 

 in France, the people catch crayfish by building huge fires 

 on the bank at night to attract them. 



