802 EMBRYOLOGY AND CLASSIFICATION. 



finement. In this stage, they ard, moreover, 

 generally too small to be readily seen in their 

 natural element. Nevertheless, this is the most 

 important period of their growth, with reference 

 to their natural affinities, and I shall take an 

 early opportunity to show how our young fishes, 

 aping the Gadoid or Blennioid type in their tran- 

 sition period, pass gradually into that of Labroids 

 and Lophioids ; how fish embryos, resembling 

 the tadpoles of frogs and toads, gradually as- 

 sume the form of Cyprinodqpts ; how A pods are 

 transformed into Jugulars and Abdominals, and 

 Malacopterygians into A^anthopterygians ; and, 

 finally, how a natural classification of the fishes 

 may be founded upon the correspondence which 

 exists between their embryonic development and 

 their structural gradation. 



In order to show further how much we may ex- 

 pect from such investigations, I will allude briefly 

 to some of the facts with which my own studies 

 have thus far made me acquainted. One impor- 

 tant truth already assumes great significance in 

 the history of the growth of animals ; namely, that 

 whatever the changes may be through which an 

 animal passes, and however different the aspect 

 of these phases at successive periods may appear, 

 they are always limited by the character of the 

 type to which the animal belongs, and never 

 pass that boundary. Thus, the Radiate begins 



