218 bulletin: museum of compakative zoology. 



a single fibril from one neuron into another. If such a conneccion 

 between nerve elements had been demonstrated beyond a doubt, thej 

 might still be considered as distinct trophic units, and the interdigitatiug 

 iibrils uniting them as the products of separate neuron cells. In the light 

 of the important discoveries of Apathy and Bethe, however, the old 

 view, that the nervous impulses are transmitted from sensory to motoi 

 neurons by the simple contiguity of their dendritic processes, may havi 

 to be abandoned for the more reasonable assumption of direct fibrillar 

 communication. 



PART II. — PHYSIOLOGY. 



As Bethe has well said, the best of anatomical knowledge concerning 

 an organ cannot be taken as certain evidence of its functions. It is 

 only after these functions have been experimentally demonstrated, that 

 we may ascribe them with confidence to the organ in question. 



Have we, then, any experimental proofs that the decapod Crustacea 

 hear] If so, is the otocyst the auditory organ ; if not, what is its func- 

 tion? These are the three chief questions which I shall attempt to 

 answer. 



A. HISTORICAL SURVEY. 



Up to the time of Delage ('87) the auditory function of the otocyst 

 was accepted, and that alone. 



Minasi (1775) promulgated the idea that Crustacea could hear. The 

 hermit crab, Pagurus, was more sensitive than man to sound vibrations. 

 The tones of a distant bell, the striking of a clock, were, according to 

 this worthy monk, perceived by Pagurus sooner than they were by 

 him. 



^lianus (1784) notes that the fishermen of his time took Pagurus 

 by means of music. 



All the older zoologists have regarded the otocyst as an organ of 

 audition. 



Hensen ('63) was the first to get experimental data. From the 

 anatomical conditions found in the otocyst of the lobster, he argues as 

 follows : Here are 468 auditory hairs upon which otoliths rest. Of 

 these hairs no two are of the same size ; they vary in a nearly continu- 

 ous series from 0.72 mm. to 0.1-4 mm. in longtli ; tlius the volume of 

 the largest is to that of the smallest as HO: 1. Comparing tlicse 



