ZOOLOGY. 543 



commences with the horny induration met with in the 

 Crab, and in the higher organized kinds of Snail. The 

 pupa is the embryonic Crab or its antetype, it is the 

 Snail in its shell. 



3296. In the third condition the Insect makes an 

 advance above the branchial condition, and casts aside 

 the Snail's or Crab's shell ; and is then the perfect Insect, 

 the Fly. 



3297. The metamorphosis is accordingly the em- 

 bryonic transition of the Insect, after extrusion from the 

 egg, through the three classes of its circle. In the ovum 

 state it only passes through that of the Intestinal and 

 Sexual animals. 



3298. This is a retrospective proof that the higher 

 animals also pass in the ovum through the condition of 

 the lower animals, but after birth through the classes 

 which directly precede them. 



What holds good of the Insects, does so also of the 

 preceding groups of animals, although in a less degree ; 

 the higher class of each circle still passes after birth 

 through one or other of the inferior classes. 



Thus, the Acalephse first appear under the form of 

 Infusoria ; next change into Polyps, and then obtain for 

 the first time the form of the perfect Acalephae The same 

 phenomenon occurs in the naked snails or Slugs. They 

 have, when freshly hatched from the egg, a small mussel- 

 like shell, which they lose at a later period. 



The Echini or Sea-urchins, which I believe ought to 

 be ranged with the Kracken, also pass through a meta- 

 morphosis. 



Finally, it is well known that the Crabs also are sub- 

 jected to a metamorphosis. Their first condition must be 

 regarded as that of the Worm. 



The law is thus universal. The second and third 

 class of every circle traverse after birth the classes, to 

 whose series they belong. 



It would even appear that the classes, also of a lower 

 circle are subject to similar changes ; at least many En- 

 tozoa, and thus the first class of the third circle, appear 



