BASIS OF THE PEOBLEM 53 



as exist among species in a state of nature between fecundity — 

 the number of ripe ova — and fertility — the number of fertihzed 

 ova — are due to failures of the gametes to meet and may be 

 called, just as the whole process may be called, ' mechanical '. 

 Such ' mechanical ' differences between fecundity and fertihty 

 may also be found in man but the chief cause of the differences 

 in the case of man is altogether of another kind and is due, as. 

 we have seen, directly to the development of conceptual thought. 



It was said above that it was proposed to show that certain 

 generahzations can be made regarding the process of reproduction 

 among species in a state of nature. This then is the first generali- 

 zation. Fecundity and fertihty are closely correlated and, ■ 

 compared with the position among men, reproduction may be 

 thought of as ' mechanical ' and even the failures to realize the 

 full power of fecundity may be thought of as ' mechanical '. 



11. It has been mentioned that fecundity is very large among 

 all species in a state of nature and we have now to ask what it 

 is that determines how large it shall be. As we have seen, the 

 fecundity is roughly measured by the number of ova produced, 

 and this number clearly depends upon many factors, such as the 

 beginning and duration of the mature period, the number of eggs 

 produced at any one time, and the length of the period between 

 the epochs of egg production. Into details of the proximate 

 causes of the differences in fecundity it is not necessary to go. 

 What it is desired to know is what factor or factors in general 

 ultimately determine the strength of fecundity in each species." 

 We may first take some examples of the degree of fecundity 

 drawn from various groups. 



The common whelk lays its eggs in capsules of which a great 

 number are produced. It has been calculated that a small clump 

 of such capsules of about two cubic inches in size contains about 

 200,000 eggs. Another mollusc, Aplysia, may lay from 2,000,000 

 to 3,000,000 at a time. ' An oyster may have sixty million eggs 

 and the average American yield is sixteen millions.' ^ The number 

 of eggs found attached to the edible crab in the breeding season 

 varies between half a million and three millions. A single pair ' 

 of flies may produce 20,000 larvae. The number of eggs produced 

 by parasites may very largely exceed these numbers. Among 

 the vertebrates the fish are the most prolific class. ' In a Ling 



' Thomson, Darwinism atid Human Life, p. 81. 



