52 Journal of Comparative Neurology and Psychology. 



Some Characteristics of the Herniit Crab. 



The genus Eupagurus is easily found in the shallower waters 

 about Woods Hole and is represented by four species, longi- 

 carpus, annulipcs, acadianus, pollicaris. E. longicarpus was se- 

 lected for the present investigation on account of its convenient 

 size (^-i^ inches in length) for aquarium purposes, and be- 

 cause of a manifestly greater brightness. Supplementary ex- 

 periments show that E. pollicaris, e. g. , learns with greater 

 difficulty. 



Members of the entire genus inhabit, under normal condi- 

 tions, the shells of gastropods, by which the abdomen is com- 

 pletely protected, the cephalothorax alone protruding. This 

 peculiar mode of life is correlated with a dextral asymmetry, 

 which extends to almost all the organs of the entire body, and 

 which shows a very nice adaptation. This favors the view that 

 the asymmetry is a result of life in dextrally spiral shells, ex- 

 emplifying at the same time degeneration. 



The establishment of the fact that these Hermits learn is 

 not surprising in view of the complexity and fineness of their 

 physiological sense apparatus, which is essentially the same as 

 that of all the Crustacea, so that it is very probable that any 

 denial of this ability to any species of the group, even upon the 

 basis of experiment, is due to incomplete or faulty methods 

 of investigation. 



Sense Organs. 



The crab has only two general kinds of sense organs, viz., 

 eyes and sense hairs, the latter of which are, however, differ- 

 entiated as to their function. These hairs, which are found in 

 all the extremities, are epithelial in nature, and are not pene- 

 trated by a nerve, but rather this latter spreads out underneath 

 each epithelial group and gives to each cell a fibril. These 

 epithelial sense cells lie in a support of "Matrixzellen," ' and 

 according to variations in their structure and especially position 

 are respectively gustatory, tactile, and auditory or "equilibra- 



^ VOM Rath, Orro. Zoologist her An zeii:er. No. 386, 1892. 



