2G8 ESSAY 01ST CLASSIFICATION. 



With the progress of growth, and in proportion as the 

 type of an animal becomes more distinctly marked in its 

 embryonic state, the plan of structure appears also more 

 distinctly in the peculiarities of that structure, that is 

 to say, in the ways in which, and the means by which, 

 the plan, only faintly indicated at first, is to be carried 

 out and become prominent, and by this the class charac- 

 ter is pointed out. For instance, a wormlike insect-larva, 

 will already show, by its trachea, that it is to be an 

 Insect and not to remain a Worm, as it at first appears 

 to be; but the complications of that special structure, 

 upon which the orders of the class of Insects are based, 

 do not yet appear; this is perfected only at a late period 

 in the embryonic life. At this stage we frequently notice 

 already a remarkable advance of the features character- 

 istic of the families over those characteristic of the order ; 

 for instance, young Hemiptera and young Orthoptera 

 may safely be referred to their respective families, from 

 the characteristics they exhibit before they show those 

 peculiarities which characterize them as Hemiptera or 

 as Orthoptera; young Fishes may be known as members 

 of their respective families before the characters of their 

 orders are apparent, etc. 



It is very obvious why this should be so. With the 

 progress of the development of the structure the general 

 form is gradually sketched out, and it has already reached 

 many of its most distinctive features before all the com- 

 plications of the structure which characterize the orders 

 have become apparent; and as form essentially charac- 

 terizes the families, we see here the reason why the family 

 type may be fully stamped upon an animal before its 

 ordinal characters are developed. Even specific charac- 

 ters, as far as they depend upon the proportions of parts 



