GftOWTS AND SEXUAL GENESIS. 459 



perfect. Here we have evidence that in animals growth 

 checks sexual genesis. And then, on the other hand, we 

 .have evidence that sexual genesis checks growth. It is well 

 known to breeders that if a filly is allowed to bear a foal, 

 she is thereby prevented from reaching her proper size. And 

 a like loss of perfection as an individual, is suffered by a 

 cow which breeds too early. It may be added, as a converse 

 fact, that castrated animals, as capons and notably cats, 

 often become larger than their unmutilated associates. 



§ 342. Notwithstanding the way in which the inverse 

 variation of growth and sexual genesis is complicated with 

 other relations, its existence is, I think, sufficiently mani- 

 fest. Individually, many of the foregoing instances are open 

 to criticism, and have to be taken with qualifications; but 

 when looked at in the mass their meaning is beyond doubt. 

 Comparisons between the largest with the smallest types, 

 whether vegetal or animal, yield results which are unmis- 

 takable. On the one hand, remembering the fact that dur- 

 ing its centuries of life an Oak does not produce as many 

 acorns as a Fungus does spores in a single night, we see that 

 the Fungus has a fertility exceeding that of the Oak in a 

 degree literally beyond our powers of calculation or imagina- 

 tion. On the other hand when, taking a microscopic pro- 

 tophyte which has billions of descendants in a few days, 

 we ask how many such would be required to build up the 

 forest tree which is years before it drops a seed, we are met by 

 a parallel difficulty in conceiving the number, if not in setting 

 it down. Similarly, if from the minute and prodigiously- 

 fertile Eotifer we turn to the Elephant, which approaches 

 thirty years before it bears a solitary young one, we find the 

 connexions between small size and great fertility and between 

 great size and small fertility, too intensely marked to be 

 much disguised by the perturbing relations that have been 

 indicated. Finally, as this induction, reached by a survey of 

 organisms in general, is verified by observations on the rela- 



