SEXUAL CHARACTERS. 101 



Cetacea, Tympanic membrane plicated. External audi- 

 tory canal long, narrow, flexible. 



Camivora, Insectivora, and Cheiroptera. External auditory 

 canal apt to be inflated at base, forming a conspicuous con- 

 vexity beneath on base of skull. The remainder of canal ia 

 membranous. 



Quadrumana. The external auditory canal entirely mem- 

 branous in New World monkeys. 



Auricle or external ear is absent in Cetacea, rudimentary in 

 Phoca (seal), and is rudimentary generally in aquatic animals, 

 as Lutra (otter), or in certain burrowers, as Talpa (mole). 

 With terrestrial mammals it attains its greatest development. 

 Commonly employed in collecting serial vibrations, it at times 

 serves as an organ of touch, as in Corynorhinus. 



XIV. 



SEXUAL CHABACTEES, 



THE reproductive function profoundly modifies the nutri- 

 tive processes of the organism. The results of such modifi- 

 cations furnish the basis for sexual characters. In the higher 

 animals the sexes can be separated by organs of generation 

 constantly present. The tout ensemble of sexual characters 

 here pertain less to the organs than to the influence exerted 

 by them upon the whole economy. But in many lower ani- 

 mals the power thus exerted by the organs over the general 

 appearance of the animal is less evident, and with some it is 

 entirely absent. With the coelenterate radiates, for example, 

 sex can be distinguished only by the increased growth of the 

 organs during periods of procreation. Indeed, in Hydra the 

 organs do not appear at any other time. 



Sexual characters are general and special. (1) General 

 characters are those maintained throughout life, and are best 



