56 READINGS IN BIOLOGICAL SCIENCE 



that among both fishes and amphibians there are species in which the eggs 

 are fertilized within the body of the female, as they are in all the higher 

 classes of vertebrate animals. But, however fertilization of eggs within 

 the body may have been originally accomplished, the process once started 

 has entailed most elaborate developments; it has led to the evolution of 

 diverse structures for the transfer of sperm cells, organs for clasping the 

 female, and the perfection of organs of sight, smell and hearing which en- 

 able the males to discover the whereabouts of the other sex. The enormous 

 eyes of the drone honeybee and the elaborately developed antennae which 

 are the olfactory sense organs of male moths are among the many evidences 

 of the influence of the function of mating upon the evolution of organs of 

 sense. When internal fertilization is once evolved, the male is confronted 

 with the problem of distinguishing the female of his own species from all 

 other kinds of living creatures. Here is one of life's hurdles which must 

 be surmounted if the species continues to exist. Consider, for instance, the 

 nuptial flight of the queen bee. When the young queen makes her first 

 flight into the air, a number of the big-eyed drones immediately start in 

 pursuit. Their course is directed not only by sight but by odor, which they 

 detect by their well-developed antennae, which are much more richly 

 supplied with sense organs than those of the queen or worker. Mating takes 

 place in the air and the process is usually fatal to the male. The sperms are 

 stored in a special receptacle in which they may Hve for years. Apparently, 

 the queen controls the outlet of this organ because eggs laid in drone cells 

 are not fertilized and hence develop into drones, while those which are 

 fertilized develop into queens or workers. In this case internal fertihzation 

 involves not only specialization of the reproductive apparatus of both sexes, 

 but the elaboration of organs in the male useful in distinguishing and fol- 

 lowing the female. The function of mating has, so to speak, put a premium 

 upon the development of activity, acuity of sense, powers of discrimina- 

 tion and special aptitudes of various kinds. It has thus been a potent factor 

 in the evolution of mind, as well as bodily organization. This is indicated 

 especially by the frequently elaborate behavior of many animals prepar- 

 atory to the act of fertilization. In birds especially, but also in certain in- 

 sects and spiders, the male performs various antics while courting the 

 female, as Darwin has described in much detail in his writings on sexual 

 selection. Courtship is obviously an activity subsidiary to the union of 

 the sexes and it has led to the development of many structural features and 

 special instincts for display. The brilliant ornamentations of male birds, so 

 wonderfully manifested in the peacock's tail and the plumage of the birds 

 of paradise, is associated with instincts for the efl:'ective exhibition of these 

 attractions. A large part of the courtship of male birds involves also the 

 employment of song. Doubtless, few people have ever reflected that the 

 voice owes its origin and at least the early stages of its evolution to its use 

 as an aid to mating. The power of making sounds is possessed in greater 



