158 Cells; or, Evolution. 



from that of the vertebrates." " No/' says Milne- 

 Edwards on the same topic, " a mollusk or an an- 

 nelid is not the embryo of a mammal arrested at a 

 certain stage of its development just as (among 

 vertebrates) a mammal is not a fish perfected. Each 

 animal carries with itself from the very beginning 

 the principle of its own specific individuality; and 

 it is a condition of its very existence that its organ- 

 ism evolve on the structural plan proper to its own 

 species." Such being the case, one type of struct- 

 ure being irreducible to another, and incapable of 

 evolving out of another, Mr. Darwin postulates 

 four of five origins for species; Haeckel and Vogt 

 likewise require several. 



175. And what does geology record ? Distinct 

 and abruptly divided origins for the main classes 

 of species, or sub-kingdoms; and, also for subor- 

 dinate types under a main one, neither an origin 

 nicely graduating from the more general one, nor 

 even an origin subsequent to it at all, or contem- 

 poraneous, but in many cases preceding it; as in the 

 echinoderms, ground pines, crocodilians just men- 

 tioned (No. -173). 



176. As to the main divisions, the first verte- 

 brates, fishes, start off suddenly in the upper Silu- 

 rian age. This probably corresponds 



* raiisi- w jth the fifth day of the Mosaic account 



1 1 on hi Types. J 



or cosmogony. No trace of links, or of 

 " a finely graduated chain," to use Mr. Darwin's 

 term, connecting the vertebrate fish with mollusk 





