288 LECTURES ON BIOLOGY 



In order to increase the sexual stimulus and make both parts 

 more eager for copulation, various arrangements have been made 

 which frequently condition a considerable difference in the 

 appearance of the two sexes. As a general rule the female 

 animals are the more passive and reserved part. In order to 

 overcome their objection, the males possess numerous means, 

 while conversely many characteristics of the female serve to 

 excite the sexual instinct of the male. Among these stimuli 

 are the scent- scales of the male butterflies, the musk-glands of 

 alligators, beavers, and civets, the anal glands of lizards and 

 snakes, and the strong broody odour of many mammals. Sounds, 

 too, play an important part in attracting the sexes and conquer- 

 ing female shyness. The autumnal forest reverberates with the 

 calling of the stag ; at the awakening of springs the songs of the 

 nightingale and finches sound from the bushes ; from the bare 

 tops of the firs the blackbird untiringly sounds its sibilant note ; 

 in the meadows locusts and crickets play their monotonous 

 tune ; and from the near pond comes in thousand voices the 

 concert of the frogs, interspersed from time to time with the 

 melancholic call of the toad. 



When dealing with sexual selection, we saw that striking 

 colours and other ornaments may serve as sexual allurements. 

 Indeed, many males assume for the ' wedding ' a special festive 

 garb and perform in addition before the females strange dances, 

 as if they hoped to charm them either by their beauty, skill, or 

 strength. During copulation snails bombard one another with 

 ' love-darts,' little daggers of carbonate of lime which are driven 

 into the male genital passage to increase the sexual desire. The 

 hook-like spicula at the posterior end of the male thread-worm 

 serves the same purpose. 



But just as the instinct of copulation produces love and affec- 

 tion between two sexes, so it causes simultaneously hatred 

 against rivals, and many animals, from the gentle dove to the 

 truculent stag, fight in the pairing period fierce and sanguinary 

 battles which sometimes end only with the death or at least 

 expulsion of the rival. The male sex is consequently furnished 

 with special weapons which are absent in females. We remem- 

 ber at once the mighty mandibles of the stag-beetle, the spurs of 

 the cock and Ornithorhynchus in this latter species a poison 



