12 INTRODUCTION TO SEXUAL PHYSIOLOGY 



Contrivances Directed Towards Gametic Union. — The contriv- 

 ances that exist to ensure the union of the gametes in fertilisation 

 are very various. Among plants the most marvellous adapta- 

 tions occur whereby pollen is transported from flower to flower, 

 sometimes by the agency of insects, sometimes by the wind. 

 Among the lower animals which live in water, on the other hand, 

 the male and female gametes are brought together very much 

 by chance, and union is only favoured by the contiguity of the 

 parent organisms. In such animals fertilisation takes place in 

 the water outside of the animal. Occasionally, however, as with 

 sponges, it occurs inside the body cavity. But in the higher 

 animals, where there is an attraction between the sexes, the 

 fertilisation of the eggs is favoured by the male following the 

 female and depositing its sperrnatozoa upon the eggs after 

 they have been laid. In the cephalopod molluscs or cuttle-fish 

 there is a contrivance of a special kind, for one of the arms of the 

 male is modified and carries the spermatozoa in packets called 

 spermatophores, and these, with the male arm, are discharged 

 bodily into the female and the sperms are set free. With some 

 fish and with the frog, though an actual copulation takes place, 

 the male embracing a female, fertilisation is still external, occur- 

 ring just as the eggs pass out of the female. The element of chance 

 is reduced still further in the higher animals in which there is a 

 definite male copulatory organ, the function of which is insertion 

 into the body of the female, whither the spermatozoa are directly 

 ejaculated, but as we have just seen the same purpose is attained 

 in the cephalopod by the discharge of the modified male arm. 

 It is noteworthy that in those animals which copulate the number 

 of ejaculated spermatozoa far exceeds the number of ova. This is 

 especially seen in mammals, where, as with man, 226 million 

 sperms may be discharged to only one ovum. 



Seasons of Sexual Activity.— it has been realised from the 

 earliest times that the vast majority of animals, as well as plants, 

 have certain recurrent seasons at which breeding takes place. 

 These seasons very often depend upon environmental conditions, 

 but apart ^rom this factor, periodicity in breeding may be in- 

 herent in the organisms themselves, a fact which, as we shall 

 see later, is clearly demonstrated in many of the higher animals. 

 Among the Protozoa the organisms appear to pass through succes- 

 sive phases of vitality which are only partly dependent upon the 



