90 MENTAL EVOLUTION IN ANIMALS. 



Fish, as we have already observed, are well provided with 

 the organs both of hearing and of smell, Amphioxus being the 

 only member of the class which is destitute of ears, and the 

 olfactory lobes in the case of some species {e.g., the Skate) 

 being of enormous size in relation to the other parts of the 

 brain. Tlie sense of touch is provided for in many species 

 by tentacular in the neighbourhood of the mouth. The soft 

 lips, and in some species the pectoral fins, are also tactile in 

 function, and in certain gurnards there are digitate appendages 

 connected with the latter which doubtless serve to increase 

 their efficiency as organs of touch. It is doubtful whether 

 taste, as distinct from smell, occurs in fish ; but we must 

 remember, as before observed, that in the case of an aquatic 

 animal tliere is no true distinction to be drawn between these 

 two senses. For as there is here no gaseous medium (like 

 the air) in question, the only distinction that can be drawn is 

 as to whether the nerve terminations, which are affected by 

 the suspended particles in the water, happen to be dis- 

 tributed over any part of the mouth where the food passes, 

 or over any other j)art of the animal. I say over any other 

 part of the animal (and not only in the nasal fosscc), because 

 in some species of fish there are embedded in the skin along 

 the sides of the body a number of curiously-formed papillae, 

 which on morphological grounds may reasonably be regarded 

 as ministering to the sense of smell, or, as we may indifferently 

 call it, of taste. H?eckel, however, speculates upon these 

 organs, and is inclined to think that they minister to some 

 unknown sense. 



The sense of sight in Amphibia and Eeptiles offers 

 nothing specially worthy of remark, except that the crystal- 

 line lens has not so high a refracting power as in Fish. The 

 transition from an eye adapted to see under water and an eye 

 adapted to see in air, appears to be curiously shown by one 

 and the same eye in the case of the Surinam Sprat. This 

 animal has its eyes placed on the top of its head, so that 

 when it comes to the surface of the water part of the eyes 

 come into the air, and " the pupil is partly divided, and 

 the lens is also composed of two portions, so that it is 

 supposed that one part of this curious eye is adapted for 

 aerial, and the other for aquatic, vision."* The senses of 

 hearing, smell, taste, and touch, although all present in the 



* Marshall, Outlines of Physiology ^ vol. i, p. 603. 



