OF MANDIBULATA. 445 



animal has to undergo, the form is entirely changed, as well 

 as the number of appendages more or less increased. This 

 is clearly a true Metamorphosis, and includes the other two 

 sorts of complete ecdj sis ; for we have here combined a to- 

 tal casting of the integuments, a developement of additional 

 appendages, such as feet or wings, and finally an entire 

 change of form. Such a combination may be witnessed 

 among the Vertebrata in Frogs, and among the Ammlosa in 

 certain Hexapod insects. Hence, in confining ourselves to 

 plain and open ecdysis, there will be no great error in stating 

 that the most imperfect takes place in the highest I'erte- 

 brata and the lowest Anmdosa ; while the most complete 

 ecdysis is that which is seen to prevail in the highest An- 

 nulosa and some of the lowest Vertebrata. 



In strict accuracy, however, it appears that we ought to 

 acknowledge the existence of complete ecdysis throughout 

 the circle of Vertebrata. Nay, some physiologists have 

 attributed insect Metamorphosis itself to a shedding of an 

 envelope analogous to that which contains the foetus of the 

 more perfect Vertebrata. As every embryo, whether ani- 

 mal or vegetable, is inclosed in a tunic more or less solid, 

 which is its chorion, so, proceeding with the analogy, they 

 conceive that there must be some condition for every ani- 

 mal, similar to the state of the foetus of the more perfect 

 animals when surrounded by the amnios ; and this state in 

 Batrachian reptiles and Hexapod insects they hold to be the 

 larva. The only danger of this reasoning is, that while we 

 find the birth of an animal to be attended with complete 

 ecdysis, we may be apt to imagine that every complete ec- 

 dysis betokens a true birth. It would however be truly 

 absurd to consider the casting of their shell by Crustacea, 

 or the periodical moulting of the serpent, in this light; yet 



