HUGH MILLER, ^ XXIX. 



votes his next and sixth chapter to the recent history, order, 

 and size of the fishes of the Upper and Lower Silurian rocks. 

 Of these ancient formations, the bone-bed of the Upper Lud- 

 low rocks is the only one which, besides defensive spines of 

 fish, contains teeth, fragments of jaws, and shagreen points ; 

 whereas in the inferior deposits defensive spines alone are 

 found. The species discovered by Professor Phillips in the 

 Wenlock shale were microscopic ; and the author of the 

 " Yestiges" took advantage of this insulated fact to support 

 his views, by pronouncing the little creatures to which the 

 species belonged as the foetal embryos of their class. Mr 

 Miller has, however, even on this ground, defeated his op- 

 ponent. By comparing the defensive spines of the Onchus 

 Murchisoni of the Upper Ludlow bed with those of a recent 

 Spinax Acanthias, or dog-fish, and of the Cestracion Phil- 

 lippi, or Port- Jackson shark, he arrives at the conclusion, 

 that the fishes to which the species belonged must be all of 

 considerable size ; and in the following chapter on the high 

 standing of the placoids, he shows that the same early fishes 

 were high in intelligence and organization. 



In his ninth chapter, on the " History and Progress of De- 

 gradation," our author enters upon a new and interesting suo- 

 ject The object of it is to determine the proper ground on 

 which the standing of the earlier vertebrata should be de- 

 cided, namely, the test of what he terms homological sym- 

 metry of organization. In nature there are monster families, 

 just as there are in families monster individuals, — men 

 without feet, hands, or eyes, or with them in a wrong place, 

 sheep with legs growing from their necks, ducklings with 

 wings on their haunches, and dogs and cats with more legs 

 than they require. We have thus, according to our author 

 — 1, monstrosity through defect of parts ; 2, monstrosity 

 through redundancy of parts ; and, 3, monstrosity through dis- 

 placement of parts. This last species, united in some cases 



