BASIS OF THE PROBLEM 45 



mean that the ova are not fertihzed. In the monkeys, however, 

 ovulation may occur independently of oestrous and in such 

 a manner that the ova then liberated may not be fertilized. 



What has so far been said all goes to show that the majority 

 of ripe ova are always fertilized among species in a state of nature. 

 There must be a certain number of failures among those species 

 which copulate, as when a mammalian female, as must now and 

 again happen, does not engage in copulation during oestrous. 

 Among species which do not copulate, failures are doubtless more 

 frequent. There is probably a greater wastage of eggs when they 

 are adhesive and fixed to some object than when they are pelagic, 

 as is most often the case among marine animals ; for when eggs 

 are adhesive the seminal fluid may drift away. 



We are now approaching a point at which it is possible to 

 establish the first generalization regarding the process of reproduc- 

 tion among species in a state of nature. It is, however, not 

 possible to make clear what it is intended to convey until some- 

 thing has been said regarding animal behaviour. Some of the 

 most striking differences between one class of animal and another 

 as regards the process of reproduction are connected with the 

 evolution of animal behaviour. So far we have spoken of instinct 

 without defining what is meant, and until something has been 

 said regarding the course and limit of mental evolution among 

 animals, the nature of the common element in all forms of 

 reproduction among all species in a state of nature and the 

 manner in which it differs from what is found among men cannot 

 be set out. It may seem that the following review is taking us 

 somewhat out of our path. It so happens, however, that in view 

 of the questions that will come up later for discussion, such a 

 sketch will be necessary and it may therefore be now undertaken 

 so as to render further amplification unnecessary. 



6. Putting aside the behaviour of plants, we find among the 

 lower animals a type of behaviour which, though simple in 

 a certain sense, cannot be adequately explained without a pro- 

 longed discussion. Some idea can be obtained of its nature if we 

 consider in what a reflex action consists. When a definite and 

 simple stimulus is followed directly by a definite and simple 

 reaction we have what is called a reflex action. This term, it may 

 be noticed, is usually restricted to cases where a nervous system 

 is present. When similar reactions occur among organisms in 



