82 ORGANS OF HEARING IN THE LOWER ANIMALS. 



On the Organs of Hearing in the Lower 

 Animals. 



The semicircular canals in the human ear (see p. 79) 

 have been supposed by some, in addition to, or apart 

 from, their functions as organs of hearing, to assist in 

 maintaining the equilibrium of the body ; at all events, 

 when they are injured, the movements frequently be- 

 come disorderly, and the otolithic organs of the lower 

 animals appear, at any rate in certain cases, to perform 

 a similar function.* 



Otolithes, as we have seen, are present in our own 

 ears, but they play a much more important part in 

 those of the lower animals. In the lowest, the sound- 

 waves may be considered to produce a certain effect 

 upon the general tissues. The soft parts of the body 

 are, however, not well calculated to receive such 

 impressions. Their effect would be heightened by the 

 presence of any solid structures, whether spicules, as 

 in sponges, etc., or solid hairs projecting from the 

 general surface, as in a great many of the lower 

 animals. 



The Medusse (jelly-fishes. Fig. 50) present round the 

 edge of the umbrella certain ** marginal bodies," with 

 reference to which there have been great differences of 

 opinion. 0. F. Miiller, by whom they were discovered, 

 regarded them as orifices for the exclusion of digested 

 food, Eosenthal and Escholtz considered them to be 

 glands, Milne Edwards as ovaries ; but it seems now 

 clearly established that some are organs of hearing, 



* Delage, "Sur une fonction nouvelle des Otocystes," Arch. c7. Zool. 

 Exp., 1887. Engelmaun, •' Ueber d. Function der Otolithen," Zool. 

 Am., 1887. 



