80 EXPLANATIONS. 



But, as the case actually stands, is this line of 

 defence more than hypothetically necessary ? The 

 lacertilia of the magnesian limestone, and these 

 labyrinthidonts of the Trias, (perhaps also of the 

 carboniferous formation,) are they so far removed 

 from fish characters as the reviewer would make 

 them ? Let any naturalist who has ever studied the 

 transmutation of the individual batrachian, pass- 

 ing in a few weeks from the branchiated fish to the 

 lunged and limbed frog or newt, its circulatory 

 and alimentary system entirely changed, say if 

 the labyrinthidon may not be the very first step 

 from some ichthyic form. What though the pro- 

 portions of the head remind Mr. Owen of the sauria, 

 and remove the animal, as he thinks, above the 

 present batrachian type ! Against any such infer- 

 ences we have the positive fact, in the organiza- 

 tion of this batrachian, of a biconcave form of the 

 vertebrae, the form peculiar to Jishes, —ar^mg, by 

 Mr. Owen's own acknowledgment, aquatic if not 

 marine habits, — also a decidedly piscine character 

 in the arrangement and even microscopic structure 



when we find a few outlying relics belonging to a class winch 

 (loi s not appear in any force till afterwards, we cannot be sure 

 that we have acquired the means of forming a distinct idea of the 

 time of the origin of that class, or the orders with which the class 

 started, as further discoveries on these points may be looked for. 



