222 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



From experiments on many different species of Crustacea, Beer ('98, 

 p. 31) concludes: " Wir haben gute Griinde, dem in Rede stehenden 

 Sinnesorgaue der Krebse statische Functionen zuzuschreiben, und liaben 

 vorlaufig gar keineu Anhaltspunkt, ihm Horfunctionen, ja den Krebsen 

 uberhaupt 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, 

 I'he 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. 



Genet^al 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 

 f^xcts, obtained by means of methyleu 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 tlie 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 ampliibious 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. 



