STUDY ON THE HABITS OF THE CRAB. 177 



may be called "senseless," but it proves that the stimulus, which 

 compels the animal to act in a definite way is a complex one and 

 that the optical side of the question plays an important role 

 therein. We did see, in fact, that the crab rushes at once 

 towards a distant sponge, if it is made conspicuous by putting 

 it into a porcelain dish. 



As in all the reactions of a crab, its behavior towards the 

 sponge varies from individual to individual. In some cases, but 

 not always, it may depend on a different activity of different 

 individuals. There are marked differences, depending on the 

 age. Older specimens are by far less active, and this bears on 

 the whole behavior. The young crabs begin their work of cutting 

 the case much sooner, the work itself is done more quickly, and 

 the cases are made more carefully. They attack very often 

 other individuals and take their cases away, which occurs only 

 rarely in larger crabs. Those observations agree with the state- 

 ment of Watson. This author found, in fact, that young rats, 

 23 days of age, possess already the faculty of performing all the 

 tasks that a rat is able to perform, in spite of their nervous 

 system being not yet definitely developed. On account of their 

 greater activity, the young rats often solve different problems 

 more quickly than the adult individuals. 



Some facts reported above confirm the conclusions of Yerkes, 

 Yerkes and Huggins, Spaulding, v.d. Heyde, Mikhailoff, con- 

 cerning the existence of associative memory in the crab. If a 

 crab carried for a long time a case of sponge or plasteline, and 

 if this case be taken off from it, the animal nearly always chooses 

 from several cases its previous one. The crab may learn to 

 come to a definite spot in the aquarium, where its sponge is 

 lying under the stones, even if this sponge be put somewhere else. 



The reported observations are somewhat fragmentary. The 

 problem of the conformity of shape of both organisms is not 

 entirely solved by them, as we do not know what may be the 

 behavior of very young crabs that are putting on a sponge for 

 the first time. The behavior after the moult also has not yet 

 been observed. Nevertheless the described facts do elucidate 

 some points of the question and, which is perhaps more im- 

 portant, they show many experimental possibilities of studying 

 the behavior of this most interesting animal. 



