2 HISTORY OF CRUSTACEA. CHAP. I. 



that these, by their cumulative force, would entirely 

 destroy the suppositions from which they proceeded, 

 even though the deductions derived from each particular 

 case might possess little of the unconditional nature of 

 mathematical proof. 



2. Secondly, the attempt might be successful to a 

 greater or less extent. If it was possible upon the 

 foundation and with the aid of the Darwinian theory, 

 to show in what sequence the various smaller and larger 

 circles had separated from the common fundamental 

 form and 'from each other, in what sequence they had 

 acquired the peculiarities which now characterise them, 

 and what transformations they had undergone in the 

 lapse of ages, if the establishment of such a genea- 

 logical tree, of a primitive history of the group under 

 consideration, free from internal contradictions, was 

 possible, then this conception, the more completely 

 it took up all the species within itself, and the more 

 deeply it enabled us to descend into the details of their 

 structure, must in the same proportion bear in itself 

 the warrant of its truth, and the more convincingly 

 prove that the foundation upon which it is built is no 

 loose sand, and that it is more than merely " an intel- 

 lectual dream." 



3. In the third place, however, it was possible, and 

 this could not but appear, primd facie, the most pro- 

 bable case, that the attempt might be frustrated by 

 the difficulties standing in its way, without settling the 

 question, either way, in a perfectly satisfactory manner. 

 But if it were only possible in this way to arrive for 



