OKGAN OF TOUCH IN MAMMALIA. 189 



filaments from the subdermal plexus. HUNTER placed his demon- 

 strations of this structure in the series of tactile organs, and 

 remarks : ' These villi are soft and pliable, they float in water, 

 and each is longer or shorter according to the size of the 

 animal. In the Spermaceti Whale they are about a quarter of an 

 inch long ; in the Grampus, Bottle-nose, much shorter ; in all 

 they are extremely vascular ; * they are sheathed in corresponding 

 hollows of the epiderm.' 



The naked skin in Cetacea is even, smooth, and polished, in 

 most instances : the numerous longitudinal plaits along the under 

 and forepart of the body in fin-whales (Bal&noptera, fig. 217, c\ 

 would allow of transverse expansion ; yet the thorax which they 

 cover needs not such provision. It is peculiar to the swifter- 

 swimming whales that pursue mackerel and herring, and may 

 serve to warn them of shoals, by appreciation of an impulse of 

 the water rebounding therefrom, and so conveying a sense of the 

 propinquity of sunken rocks or sand-banks. Sensitiveness to 

 movements of the ambient ocean is indicated by certain observed 

 phenomena. Thus whale-fishers aver that when a straggler is 

 attacked its fellows will bear down from some miles' distance, as 

 if to its assistance ; and it may be that they are attracted by per- 

 ception of the vibration of the water caused by the struggles of the 

 harpooned whale or cachalot. But, in the main, tactile or discrimi- 

 native sensibility is very low in the Cetacean order. The thick 

 hard and short vibrissa3 on the lips of Sirenia, appear to relate 

 rather to prehension than exploration of food. 



The extent of surface and delicate organisation of the parts of 

 the skin forming the wings and ear-conchs of those of the Bat- 

 tribe that pursue volant insects (vol. ii. fig. 156), and the an- 

 tennal nose-leaves of many species (Rhinolophidce), relate to the 

 perception of atmospheric impulses rebounding from surfaces near 

 which the Bat approaches in flight. Thus, when deprived of 

 sight, and with the ears and nostrils plugged up, as in Spallan- 

 zani's questionable experiments, he avers that the Bat was capable 

 of directing its flight with the same security and accuracy as 

 before, guiding its course through passages just large enough to 

 admit it without coming into contact with the sides, and even 

 avoiding numerous small threads which were stretched across the 

 room in various directions, the wings never touching any of them. 

 The delicate sensibility of the membranous integument meets all 

 the conditions of the crepuscular or nocturnal flying of the bat, 

 without involving a new and peculiar ' sixth sense,' as deduced 



1 xx. vol. iii. p. 57, nos. 1403-1405. 



