liO THE INDUCTIONS OF BIOLOGY. 



dividuals ; and among the highest fishes, as sharks, the 

 eggs»are comparatively few and comparatively large. Rep- 

 tiles have eggs that are smaller in number, and relatively 

 greater in mass, than those of fishes ; and throughout this 

 class, too, there is a general ratio between the bulk of the egg 

 and the bulk of the adult creature. As a group, birds show 

 us a further limitation in the number of their eggs, and a 

 further increase in their relative sizes ; and from the minute 

 eggs of the humming-bird up to the immense ones of the 

 Epiornis, holding several quarts, we see that, speaking ge- 

 nerally, the greater the eggs, the greater the birds. Finally, 

 among mammals (omitting the marsupials) the young are 

 born, not only of comparatively large sizes, but with ad- 

 vanced organizations ; and throughout this sub-division of 

 the vertebrata, as throughout the others, there is a mani- 

 fest connexion between the sizes at birth and the sizes at 

 maturity. As having a kindred meaning, there 



must finally be noted the fact, that the young of these 

 highest animals, besides starting in life with bodies of 

 considerable sizes, almost fully organized, are, during sub- 

 sequent periods of greater or less length, supplied with nutri- 

 ment — in birds by feeding, and in mammals by suckling and 

 afterwards by feeding. That is to say, beyond the mass and 

 organization directly 'bequeathed, a bird or mammal obtains 

 a further large mass at but little cost to itself. 



"Were an exhaustive treatment of the topic intended, it 

 would be needful to give a paragraph to each of the many 

 incidental circumstances by which growth may be aided or 

 restricted. Such facts as that an entozoon is limited by the 

 size of the creature, or even the organ, in which it thrives ; 

 that an epizoon, though getting abundant nutriment with- 

 out appreciable exertion, is restricted to that small bulk at 

 which it escapes ready detection by the animal it infests ; 

 that sometimes, as in the weazel, smallness is a condition to 

 successful pursuit of the animals preyed upon ; and that at 

 other times, the advantage of resembling certain other crea- 



