44 SHELLS AND SHELL-FISH. PART I. 



lengthened, and the legs and feet so small as to be rudi- 

 mentary ; while the Coscilia have neither feet nor bran- 

 chia, and sometimes are without eyes. This group, 

 therefore, among the Fertebrata, is precisely the sort of 

 point or nucleus from which diverge two distinct series 

 of animals : the one leads to the serpents, or reptiles ; 

 the other branches out, in an opposite direction, to the 

 fishes ; but both these ultimately meet in the ostrich, 

 which exhibits a union of the bird and the quadruped. 

 Each of the five divisions of the vertebrated circle afford 

 parallel instances ; so that we invariably find the most 

 aberrant group is always that which is the least or- 

 ganised ; just as is the class Acrita in the whole animal 

 kingdom. The annulose Vermes, as the tape-worms, 

 and other intestinal creatures still more simple, forming 

 the Tanioides of Cuvier, are, in the annulose circle, 

 precisely what the amphibians become in the Vertebrata. 

 They exhibit the first simple outlines of that structure 

 which terminates in the painted butterfly and the sa- 

 gacious bee ; and, when nature has reached these points 

 of perfection, she returns, by slow degrees, through the 

 Annelides, or red-blooded worms, to the same point, 

 although by a different route. Such, also, will be 

 found her course in the testaceous class. The Paren- 

 chymata, or parasitic Mollusca, may be considered the 

 first indistinct and incipient developement of the Tes- 

 tacea, the point from which nature diverges towards 

 the phytophagous gastropods on one side, and to the car- 

 nivorous gastropods on the other, until both these series 

 meet together, and form a perfect circle in the family 

 of TurbidcB. It will subsequently appear that this re- 

 markable principle of variation is not merely confined 

 to the first great circle formed by the Testacea ; it is 

 abundantly evident in its primary divisions nay, in 

 some instances, even in its families. Among the Ce- 

 phalopoda it is particularly strong. All writers who 

 have mentioned the Foramimfera, so admirably and 

 beautifully investigated by D'Orbigny, hesitate not to 

 place these microscopic atoms in that order, although it 



