66 CREATIVE EVOLUTION 



Let us place side by side the eye of a vertebrate 

 and that of a mollusc such as the common Pecten. 

 We find the same essential parts in each, composed of 

 analogous elements. The eye of the Pecten presents 

 a retina, a cornea, a lens of cellular structure like 

 our own. There is even that peculiar inversion of 

 retinal elements which is not met with, in general, 

 in the retina of the invertebrates. Now, the origin 

 of molluscs may be a debated question, but, what 

 ever opinion we hold, all are agreed that molluscs 

 and vertebrates separated from their common parent- 

 stem long before the appearance of an eye so complex 

 as that of the Pecten. Whence, then, the structural 

 analogy ? 



Let us question on this point the two opposed 

 systems of evolutionist explanation in turn the hypo 

 thesis of purely accidental variations, and that of a 

 variation directed in a definite way under the influence 

 of external conditions. 



The first, as is well known, is presented to-day in 

 two quite different forms. Darwin spoke of very 

 slight variations being accumulated by natural selection. 

 He was not ignorant of the facts of sudden variation ; 

 but he thought these &quot; sports,&quot; as he called them, were 

 only monstrosities incapable of perpetuating them 

 selves ; and he accounted for the genesis of species by 

 an accumulation of insensible variations. 1 Such is still 

 the opinion of many naturalists. It is tending, how 

 ever, to give way to the opposite idea that a new 

 species comes into being all at once by the simultaneous 

 appearance of several new characters, all somewhat 

 different from the previous ones. This latter hypo 

 thesis, already proposed by various authors, notably 



1 Darwin, Origin of Species, chap. ii. 



