222 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
From experiments.on many different species of Crustacea, Beer (’98, 
p- 31) concludes: ‘* Wir haben gute Griinde, dem in Rede stehenden 
Sinnesorgane der Krebse statische Functionen zuzuschreiben, und haben 
vorlaufig gar keinen Anhaltspunkt, ihm Horfunctionen, ja den Krebsen 
iiberhaupt Gehorsinn, zuzuschreiben.” 
Hensen’s statement that the free auditory hairs of Mysis vibrated to 
different musical notes is simply an interesting physical fact. Hairs on 
the back of one’s hand will do the same, but they are not auditory. 
The true sense of hearing is lacking not only in Crustacea, but probably 
in all other water-inhabiting animals lower than Amphibia, especially in 
invertebrates. 
Beer thus comes back to the opinion of Johannes Miiller (’37) ex- 
pressed sixty years before: That in most invertebrates we find nothing 
comparable to the ear; and any reaction to sound vibrations should be 
attributed to a tactile rather than to an auditory sense. 
A few months later Beer (’99) brought out a second paper, describing 
his experiments with blind shrimps, and answering a criticism of his pre- 
vious work by Hensen (99). Here the auditory sense, he urges, ought 
to be intensified, all possibility of sight entering as a factor into the 
experiments being effectually eliminated. The conclusions reached by 
him in his earlier work are verified in this. 
General Criticism. 
It is a noteworthy fact, that in the experimental work done to deter- 
mine the function or functions of the otocyst, few of the investigators 
have acquainted themselves with the finer structure of the organ under 
consideration ; one of the essentials for successful physiological work is a 
complete knowledge of the anatomical side of the subject. This is well 
illustrated in Bethe’s work on the brain of Carcinas, where anatomical 
facts, obtained by means of methylen blue, laid the groundwork for his 
later confirmatory experiments. 
Since the dissections by Hensen, little or no morphological work has 
been done on the otocysts of the Brachyura, yet a deal of physiological 
work has been attempted. 
The experiments of Beer are beautifully worked out, and logical in 
sequence ; yet, while he tried experiments on water-inhabiting animals, 
no attempt was made to experiment on amphibious decapod Crustacea, 
such as the fiddler crab. These animals, spending, as they do, a good 
share of their life on land, would certainly have more need of an auditory 
organ than decapods which are always beneath the surface of the water. 
