Classification in Zoology. 233 



in the animal kingdom, would, in the present, contribute 

 more to the advance of zoology than any amount of descrip- 

 tion of new species. 



But these investigations of young animals should be made 

 with a full knowledge of their various relations, and with the 

 view of ascertaining chiefly these zoological peculiarities, 

 which may illustrate more fully the value of all these 

 relations. 



There is another field of investigation, hardly yet entered 

 upon, which is likely to contribute largely to the improve- 

 ment of our classification. I refer to the study of fossils, 

 compared in their structural peculiarities with the embryos 

 of their living representatives. It has already been shown 

 that many fossils of the earliest geological periods have a 

 close resemblance to embryonic forms of the present day ; 

 and that, in their respective families, these fossils rank 

 among the lower types. 



This result, in itself, should be a sufficient inducement to 

 trace this double relation, and to ascertain, from as many 

 fossils as possible, whenever they are sufficiently well pre- 

 served to allow of such comparisons, what is the extent of 

 their analogy to embryonic forms of the present period, and 

 also what is the amount of affinity they have to the lower 

 types of their respective classes. 



I would mention, in this connection, the necessity of a re- 

 vised comparison of the Trilobites, with the earliest stages of 

 development of Crustacea, when it will be found, as I have 

 already seen it, that almost all the genera of Trilobites seem 

 to be the prophetic images, in a gigantic form, of the different 

 types the Crustacea present in their embryonic state. The 

 different degrees of development of their different types, when 

 contrasted with each other, will go far to assign to each 

 genus, its appropriate rank, I venture even to say, that the 

 time will come when the relative age of fossils, within cer- 

 tain limits, will be as satisfactory a guide in assigning them 

 their normal position in a natural system, as the facts de- 

 rived from the study of their structure, — so intimate are the 

 connections existing between all parts of the wonderful plan 

 displayed in creation. 



Little or no advantage has as yet been derived from the 



