Mr Lillie, Notes on the Larger Cetacea. 351 



In the case, however, of the Rorquals Balaenoptera sihhaldii 

 and Balaenoptera musculus some ten individuals of each species 

 were examined and it was found that a definite distribution of 

 hairs could be made out in each case. Four rows of white, bristle- 

 like hairs from half an inch to an inch in length occur on the 

 dorsal surface of the beak or facial region of the head. These 

 consist of two inner rows on either side of the median ridge which 

 bears the blowholes or external nares and two outer rows following 

 the edges of the snout, from points just behind the blowholes to 

 its anterior extremity. The average number of hairs in each row 

 is about eight. 



On each side of the lower jaw there was a row of some five or 

 more hairs running from the tip of the mandible along the middle 

 line of the outer edge of each ramus to a point just in front of 

 the eye. At the extreme anterior end of the mandible, over the 

 ligamentous junction of the rami, there were also two rows of hairs 

 set at right angles to those above mentioned. These occur close 

 together and run parallel to each other from the upper to the 

 under surface of each ramus. The hairs in these two rows are 

 placed closer together than in the others, there being generally 

 about fourteen hairs in each row. 



On looking through the Cetacean literature there appears to be 

 no record of the occurrence of hairs in the odontocetes, except in 

 some foeti. It would seem that the presence of hairs in the adult 

 is restricted to the whalebone whales and their retention and 

 distribution over the beak and mandible in these forms may 

 be due to their possessing a tactile function and thus serve to 

 indicate to the animal the presence of its food. 



The small size of the organisms, which generally form the food 

 of the Mystacoceti, making them difficult to see, and the olfactory 

 organs of the Cetacea being very reduced, it seems reasonable to 

 suppose that the occurrence of tactile hairs over the oral region 

 would be a distinct advantage, as the small food animals would 

 brush against them and thus inform the whale when to open its 

 mouth. The top of the snout of a whale is, after all, only the 

 prolonged upper lip, where one would naturally look for vibrissae. 

 The food of the odontocetes being of a larger size the presence of 

 tactile hairs is not obviously required, and so the hairy covering 

 has entirely disappeared in the adult forms of these whales. If 

 the hairs of the whalebone whales do not function as suggested 

 above, an interesting problem remains open to solution to explain 

 how these animals become aware of the presence of their food. 



