Chap. III.] OF SENSE ORGANS. 65 



low degree by most invertebrate animals. Even the most 

 perfect form of the organ of hearing among these 

 animals is but a very rudimentary structure. In this 

 respect a great difference exists between the sense of 

 Sight and that of Hearing. Whilst the eye of the 

 Cuttle-fish attains a degree of elaboration not falling so 

 very far short of the most perfect form which the organ 

 displays among vertebrate animals, the organ of hearing 

 throughout the Invertebrata is remarkable for its sim- 

 plicity, and remains in all of them notably inferior to the 

 very high type attained by this sensorial apparatus in 

 many Mammals and in Man. 



Like the sense of Sight and the sense of Smell, that of 

 Hearing, even in its simplest grades, serves to bring the 

 organism into relation with more or less distant bodies. 

 It is only necessary that these latter should be capable of 

 transmitting sonorous vibrations through water or air to 

 the auditory organs which become attuned to receive them. 



It seems just possible, however, that the so-called 

 * auditory saccules ' of the Invertebrata, may have more 

 to do with the ' sense of Direction,' or of the organism's 

 relations with space, than with the sense of Hearing.* In 

 Vertebrate Animals, it would appear, that both these 

 functions are associated with the auditory apparatus, and 

 it is by no means certain that the ' sense of Direction,' or 

 of the organism's space-relations, may not be an endow- 

 ment more primordial than that of Hearing. 



No auditory perception seems to be present at all — 

 certainly none has as yet been detected or inferred to exist 

 — in many of the lower forms of life ; while in other 

 animals, though possibly existing, its organs remain as yet 

 unrecognized. The latter condition obtains, for instance, 

 with the majority of Crustacea, Spiders, and Insects. 

 * See p. 218. 



