270 Professor Pictet on the Distribution of Fossils. 



in animals ; it is consequently true in a very vague sense ; 

 but I believe it to be altogether inadmissible if we particu- 

 larize it, and if we understand by it that beings form a single 

 and continuous series. It is impossible to place all living 

 animals in such an order that we may always pass from 

 one species to another by following a decrease in perfection. 

 This is not the place to discuss, at full length, a theory 

 known to every zoologist. I shall satisfy myself by refer- 

 ring to two classes of numerous facts opposed to its admis- 

 sion. On the one hand, there are classes of animals so in- 

 sulated that nothing connects them with others, a circum- 

 stance which creates inevitable breaks and interruptions in 

 this pretended series : thus the birds have no intermediate 

 object which could unite them either to the mammifera or 

 the reptiles. On the other hand, there are types of organi- 

 zation which are absolutely indivisible, and of which the 

 most perfect beings are superior to the mean of another 

 type, while the most imperfect are inferior to it : thus the 

 molluscs, in the instance of the cephalopods, are superior to 

 the articulated animals, and they are inferior to them in the 

 case of the acephala ; we cannot, therefore, arrange the mol- 

 luscs and the articulata in a single series. Besides, the per- 

 fection of these same types consists in the realization of the 

 conditions of a certa,in organism, which renders it very diffi- 

 cult to compare them with each other. The mollusc, the ar- 

 ticulated, and the radiated animal of the highest rank, have 

 each characters of perfection of a different kind, which do 

 not always allow us to decide that one is superior to another. 

 We do not, then, admit a scale of beings as a ground- 

 work in the discussion of this law. It appears to us, that 

 the idea which ought to be formed of the true relations of 

 animals, when viewed in regard to their perfection, is the 

 following. These beings are divisible into a certain number 

 of groups, each of which realizes a particular type. Some 

 of these groups are evidently Superior to others in their or- 

 ganization, viewed as a whole ; but sometimes, also, the com- 

 parison of them does not enable us to establish a real supe- 

 riority. The most perfect type is that of the vertebrata, 

 which ought evidently to be placed far above all the groups 



