PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 169 



To throw more light on our knowledge of the vertebrate ear, com- 

 parative study of the (perhaps) analogous organ found among inverte- 

 brates may be of great practical value. For by such comparative 

 study zoologists have been enabled to solve many perplexing questions 

 which might otherwise have proved too diflficult for solution. 



The present study was undertaken with this practical bearing of the 

 subject in mind, and with the hope that by the aid of modern neurologi- 

 cal technique it would be possible to go deeper into many undecided 

 questions than Hensen could. 



The work is necessarily twofold in its scope, owing to the inseparable 

 nature of the morphology and physiology of the auditory organ. We 

 have, first, to obtain more accurate knowledge concerning the structure, 

 innervation, and development of the decapod otocyst. In doing this 

 especial attention must be given to the innervation, which must be com- 

 pared with that of other sense organs in decapods. And, secondly, 

 we must determine from evidence obtained by others in the past, and 

 from additional physiological experiment, whether we are justified in 

 ascribing a true auditory function to this much discussed apparatus. 



PART I. — MORPHOLOGY. 



A. HISTORICAL SURVEY. 



Although the literature up to Hensen's time is well summarized by 

 him, yet it may be worth the while to take a glance at what has been 

 done, touching upon only the more important works, however, as a fairly 

 complete list of authors is appended in the Bibliography. 



The earliest notice of an ear in Crustacea is that of Minasi, a Domini- 

 can monk, who in 1775 attributed the sense of hearing to Pagurus, the 

 hermit crab, and described as the auditory apparatus what is now known 

 as the green gland or excretory organ of decapods. The organ supposed 

 to subserve the function of hearing was thus from the very first mis- 

 placed, and its identity was in doubt even up to the time of Hackel 

 ('57) and Leydig ('57), who were the first to rectify the erroneous ideas 

 which existed in regard to the functions of the green gland and the 

 otocyst. 



The true sacs were, however, discovered and described as early as 

 1811 by Rosenthal ('11). He mentions the cavity, its opening, and 

 nerve; but it was left for Treviranus ('02-'22, Bd. 6, pp. 308-310) to 

 discover the sand, or otoliths, present in the otic chamber. 



