Habits, Reactions, and Associations in Ocypoda arenaria. 1 1 



Whether one calls it taste or chemical sense, there is no doubt that 

 Ocypoda is able to distinguish between foods. When several different kinds 

 of food are presented to a number of individuals, certain kinds will be eaten 

 in preference to others. 



A rather interesting experiment was one where the feeding was observed 

 in the case of an individual from which the small chela had been cut oft" close 

 to the body. This specimen seemed to have great difficulty in adjusting a 

 fish so that it could be eaten. An attempt was made to use the first ambu- 

 latory appendage on the side from which the chela had been removed, but 

 the crab was not very successful in this, and after many trials it hit upon the 

 following method: The fish was grasped about in the middle with the large 

 chela in such a manner that the end was directed toward the mouth, and in 

 this position feeding was accomplished with some difficulty. It would push 

 the end of the atherina up against the mouth-parts, where the mandibles 

 would take hold and then pull the fish away, thus tearing off pieces which 

 could be eaten. This was repeated many times on different occasions. 



Occasionally the " sand-crab " did not seem to be able to adjust the fish 

 according to this method, and then holding the atherina with its one chela 

 tightly against the sand, it tipped the body downward until the mouth-parts 

 were in contact with the fish, when it proceeded to feed as usual. 



"OLFACTORY ORGANS." 



Nagel (1894) and Bethe (1895, 1897) have studied the crustacean Car- 

 cinus mmias in the endeavor to find out in how far this crab makes use of 

 the senses of smell and taste, or, as these have been called together, the 

 " chemical sense." Both of these investigators have concluded that Car- 

 cinus in its search for food is aided by the chemical sense, and Bethe has gone 

 so far as to say that the chemical stimuli are the principal ones that lead the 

 crab to food, the eyes aiding only slightly or none at all. The experiments 

 devised and the observations made, as recorded below, were for the purpose 

 of determining if Ocypoda would react to foods at a distance through other 

 senses than that of sight. 



The so-called " olfactory organs " of Ocypoda are situated on the an- 

 tenna:, which are very much reduced in size (plate 4, fig. c). They consist 

 of the typical " olfactory hairs," which are open at the distal end and which 

 have a nerve running part way up the axis. These hairs are not as numer- 

 ous as the feathered tactile hairs which occur in a large bunch on the seg- 

 ment next to the basal segment of the antenna. 



Dr. Mayer observed that ocypodas dug up decomposing fish which had 

 been placed about the roots of young pineapple-plants, but this does not prove 

 that the odor attracted them, for it is quite probable that the juices or small 

 particles of the fish were left on the surface of the sand and that the ocypodas 

 in their wanderings and search for food happened to pass over these places. 



