THE REPRODUCTIVE POWER IN ANIMALS. 51 



explanation of this yariation in the conditions under which the 

 young develop. These insects are a common prey for other ani- 

 mals, especially birds, which devour them in great numbers, their 

 exposed condition upon the surface of leaves rendering them easily 

 obtainable. Hence it is that of the total number of ova produced 

 only a very small proportion result in an increase of their kind, 

 the young insect being devoured before completing maturation. 

 This extraordinary and anomalous increase of the reproductive 

 power thus furnishes an extreme instance of the operation of the 

 law under consideration. 



The Oyster. It is well known that the oyster is very pro- 

 lific. A single individual may produce over a million young. It 

 is generally known, too, that this animal has many natural ene- 

 mies, the most destructive being the star-fish. It is obvious that 

 the reproductive power is here in relation to the unfavorableness 

 of the natural environment, and especially during the embryonic 

 period, when the body is small and less adequately protected, being 

 destitute of a shell in the earliest stages. 



The Codfish. While most fishes produce eggs in great 

 numbers, the cod is especially remarkable in this respect, a single 

 female depositing annually eight or nine millions. The liability 

 of destruction of the ova and young is perhaps at its maximum 

 here, there being many natural enemies and very slight means of 

 defense. The application of the law is obvious. 



It seems unnecessary to bring forward other instances to show 

 that the law holds good when the conditions of embryonic life are 

 unfavorable. While it can not be so strikingly shown when the 

 opposite conditions prevail when the circumstances of embry- 

 onic life are favorable it scarcely seems doubtful that it is less 

 applicable here. When animals have abundant food-supply and 

 ample protection against their foes and against exposure to weath- 

 er, etc., the reproductive function is generally only moderately 

 active. Without citing particular instances, it may be sufficient 

 to point out that the largest and most intelligent animals those 

 that are strongest in body and quickest in instincts, and thus 

 best able to defend themselves and their young against their ene- 

 mies and to secure food and shelter are the least prolific, bring- 

 ing forth young at longer intervals and in fewer numbers. 



It may have occurred to the reader that while there thus seems 

 to be a law governing the procreative power in animals, this law 

 is yet subordinate to another more general, more fundamental 

 law the law of the preservation of the species. Nature guards 

 against the destruction of her works, and the instances of excessive 

 activity of the reproductive function we have noted are to be in- 

 terpreted as efforts made in the economy of nature to save the 

 species from extinction. 



