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 zodlogists have been enabled to solve many perplexing questions 
which might otherwise have proved too difficult 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 Hickel 
(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. 
