ISO EDWIN B. POWERS. 



Sometimes they lie concealed in short burrows along the banks 

 (Harris, '03). C. virilis is found to be absent from the muddier 

 and shallower portions of the streams but is sometimes taken in 

 ponds with C. immunis (Harris, '01), but is more often found in 

 running streams, among the rocks of the more rapid portions 

 (Harris, '03). They do not burrow except when the ponds 

 begin to dry or winter approaches. Garman ('89) took this 

 species from wells, Wilson's cave and streams. C. diogenes is a 

 burrowing species and often makes mud chimneys, often burrow- 

 ing in damp ground some distances from the open water, which it 

 seldom enters except during the breeding season (Pearse, '10). 

 C. immunis is a mud-loving species and is found mostly in small 

 pools, though it sometimes occurs in brooks and rivers (Pearse, 



/. c.} (Harris, '03). 



4. Senses. 



The fact that crayfishes are sensitive to chemicals has been 

 shown by several authors. Putnam ('75) noted that C. pelluci- 

 dus, the blind crayfish, will hunt food when it is thrown into the 

 water. Holmes and Homuth ('10) found that the whole body is 

 more or less sensitive to olfactory stimuli, and that the antennae, 

 mouth parts and tips of the chelipeds are sensitive in the order 

 named. Nagel ('94) observed the chemical sense in Astacus. 

 Wright ('84), by a study of the antennules of C. propinqmts, 

 found that five of the eighteen segments, i. e., eleven to fifteen 

 inclusive, bear eight of the so-called olfactory organs and the 

 distal nine fewer. Bell ('06) found that the crayfishes with 

 which he worked reacted positively to meat juice and negatively 

 to lavender water, acids and salts, and concluded that they are 

 sensitive over the entire body but more in the anterior appendages 

 than in other parts. Chidester ('12) found when meat was 

 thrown into the water that crayfishes would approach and seize 

 fresh meat quicker than they would meat dried in the air. 



III. THE SENSING OF CARBON DIOXIDE AND ACETIC AND 



HYDROCHLORIC ACIDS. 



The crayfishes sensed the carbon dioxide and acetic and hydro- 

 chloric acids when passing into the high acid concentration end 

 of the experiment tank. This was indicated by certain specific 



