7596 Notices of New Books. 



the skulls of oviparous Vertebrata, the elasticity of the skulls of which 

 would be objectless ; and iu them it cannot have been the inhe- 

 rited evidence of an aborted function previously matured, by natural 

 selection, in a viviparous race, which, being higher in the scale of 

 organization, on the theory of natural progression would be developed 

 from and subsequently to the ovipai'ous. They must, then, clearly 

 be considered as one of the numerous examples of unrelated resem- 

 blances and " unity of type," upon which we are led to doubt that 

 common resemblances are dependant on genealogical relationships. 

 A great difficulty, in attributing progress of organization as the result 

 of the gradual modification and advancement of organs, through cer- 

 tain slight variations giving their possessors advantages over their 

 fellows, exists in the fact that small measures of improvement of many 

 organs, or anything short of their immediate perfection, would confer 

 no advantages on their possessors. How, for example, could mammi- 

 ferous nutrition have been perfected by short stages ? The young 

 mammal requires a certain amomit of nourishment for its existence, 

 and it is obvious it could not live during the imperfected stages of 

 Ihe organs of supply ; so that, however rapid the strides of improve- 

 ment might be, the extinction of the improved progeny would at once 

 prevent the results of the improvements being accumulated and 

 realized ; and it is impossible to fancy a process of generation inter- 

 mediate between the oviparous and viviparous, to account for the 

 gradual adaptation of the young to suit the gradual perfection of the 

 milk-producing organs. 



In the competitive struggle for existence individuals having the 

 greatest natural stamina, and the usually accompanying repro- 

 ductive energy, would certainly have the advantage ; and would 

 not these qualities compete with and extinguish all other deviations 

 from the normal condition ? Now, as a general rule, we think 

 it must be assumed that no marked deviation from the normal 

 standard takes place without some sacrifice of reproductive energy, 

 either iu animals or plants ; and, parallel with this, the strongest 

 individuals have alwa}S the characteristic points of the genus or 

 species most strongly developed ; for instance, who would think of 

 taking a small and weakly specimen — the leaf of a young seedling, 

 or the first-developed small frond of a fern — to describe the charac- 

 teristic features of the species from? Have we not, therefore, on 

 this principle, a natural provision for perpetuating the individuality 

 of species, by giving the n)ost normal individuals the advantage iu 

 the struggle for existence ? 



