PALEONTOLOGY 99 



He refers to change of climate, migrations and loss 

 of geological record as accounting for " those sweep- 

 ing changes, not only of species, but even of genera, 

 families, and orders which characterize the passage 

 from one great era to another. ' ' 



" But this does not explain the apparent discontin- 

 uity between consecutive species in the same locality 

 in continuous, comformable strata, or the rarity of 

 transitional forms when one species takes the place of 

 another in an apparently continuous record. In such 

 continuous deposits the successive faunas do indeed 

 graduate insensibly into one another, but apparently 

 as in contiguous geographical regions, by substitution, 

 not by transmutation." 



From this it is evident that in some cases he regards 

 the record as being comparatively complete, and not 

 extremely fragmentary, and it is admitted that in this 

 record the transitional forms between species are 

 absent. The reason why they are not found is, ac- 

 cording to him, that, for the most part, they never 

 existed, owing to the fact that the formation of 

 species takes place very rapidly, in which case few 

 connecting links are required. 



His idea is that heredity resists change of form 

 until circumstances either compel it to give way, re-- 

 suiting in the evolution of new species better adapted 

 to the environment than the old, or, on the other 

 hand, in the destruction of the species if they do not 

 change sufficiently. 



This paroxysmal theory of the origin of species 

 is opposed to Darwin's idea of slow and imperceptible 

 changes. 



The absence of intermediate forms between species 

 has led Le Conte to advance this theory. Instead of 

 requiring many generations to form a new species, as 

 is taught by most evolutionists, perhaps one or two, 



