154 THE LAW OF BIRTHS AND DEATHS 



conditions plants not only fail to produce fertile seed, 

 but sometimes they also fail to flower, as the extract 

 from Darwin given in a previous chapter shows. There 

 is also the case of the worker bee, which might, how- 

 ever, be reasonabty quoted in favour of the opposite view 

 that failure of ovulation is produced by unfavourable 

 conditions, since the diet of the worker is much sparser 

 and plainer than that of the queen. In the case of the 

 domestic fowl, not only are the eggs less fertile when the 

 birds get insufficient exercise, but fewer eggs are laid, 

 and this seems to mean that fewer egg cells are produced 

 at ovulation. Some fowl-keepers assert, however, that it 

 is impossible to feed laying hens too highly provided that 

 they receive plenty of exercise, and failure of ovulation 

 in the case of individuals receiving insufficient exercise 

 may be the result of unhealthy conditions. 



In the case of wild animals in captivity which produce 

 smaller litters, this might be due either to fewer egg cells 

 being produced at ovulation or to fewer being fertilised. 

 It might also be urged that if ovulation is more prolific 

 under favourable conditions while fertilisation is more 

 difficult, the two principles would in large measure cancel 

 each other. Thus, as egg cells vary in receptivity, a de- 

 crease in the average receptivity might be compensated 

 by an increase in the number of egg cells, which would 

 increase the chances of fertilisation. But this could only 

 compensate a decreased receptivity to a small extent. 



While the weight of evidence and of probability seems 

 to favour the view that ovulation is merely a specialised 

 form of asexual reproduction, yet it will be best to leave 

 this an open question. It is not one which can be settled 

 by deduction or analogy, and the amount of evidence 

 at present available is not sufficient to justify a decision. 

 Possibly the solution will be found in the application 

 of the principle of the vital optimum to ovulation. 



