270 ESSAY ON CLASSIFICATION. 



It seems to me that these facts are likely to influence 

 the future progress of Zoology, in enabling us gradually 

 to unravel more and more distinctly the features which 

 characterize the different subordinate groups of the animal 

 kingdom. The views I have expressed above, of the 

 respective value and the prominent characteristics of these 

 different groups, have stood so completely the test in this 

 analysis of their successive appearance, that I consider 

 this circumstance as adding to the probability of their 

 correctness. 



But this has another very important bearing, to which 

 I have already alluded in the beginning of these remarks. 

 Before Embryology can furnish the means of settling 

 some of the most perplexing problems in Zoology, it is 

 indispensable to ascertain first what are typical, class, ordi- 

 nal, family, generic, and specific characters; and as long 

 as it is supposed that these characters appear neces- 

 sarily during the embryonic growth, in the order of their 

 subordination, there is no possibility of deriving from 

 embryological monographs that information upon this 

 point so much needed in Zoology, and so seldom alluded 

 to by embryologists. Again, without knowing what con- 

 stitutes truly the characters of the groups named above, 

 there is no possibility of finding out the true characters of 

 a genus of which only one species is known, of a family 

 which contains only one genus, etc.; and for the same 

 reason no possibility of arriving at congruent results witli 

 reference to the natural limitations of genera, families, 

 orders, etc., without which we cannot even begin to builct 

 up a permanent classification of the animal kingdom, and, 

 still less, hope to establish a solid basis for a general com- 

 parison between the animals now living and those which 

 have peopled the surface of our globe in past geological 

 ages. 



