40 Dr. A. S. Packard, Jr's Revision of the 



individual, but of a large mass, whose separate peeularities agreeing in 

 the main, are combined into a "composition" or diagnosis. Nature 

 thus constantly eludes our grasp, and after all nothing but a picture of 

 the flitting form remains impressed upon the mind which we embody 

 in an idealized form in words. 



Also, in being compelled, in print, to treat of genera as if they were 

 arranged in a continuous line from the highest to the lowest, one fails 

 in expressing clearly to others his views as to the true relations of the 

 groups. Thus we have to stop in our ascending series to interpolate 

 aberrant forms, which must be described at this point, if anywhere, as 

 the systematist is constantly drawn aside to deal with groups which 

 stand out of the apparently normal succession of organized beings, 

 consisting of degradational forms, and connecting links between mem- 

 bers of a somewhat linear series, and outstanding genera difficult to 

 locate. The ascending series is at times disturbed by constellations of 

 forms which are so complexly grouped as to so divert the attention 

 that it is difficult to take up the thread conducting to the close of the 

 series. To our mind there must be a compromise between those natu- 

 ralists who believe that all groups are "artificial," or in a state of un- 

 stable equilibrium, thus constantly changing their value ; and those 

 naturalists, on the other hand, who believe genera, families, orders and 

 classes to be very easily limited, defined, and thus always recognizable 

 from such definitions. Where an order is defined as depending on 

 "complication of structure,"* and families on "form," genera on de- 

 tails of structure, and species as depending on proportion and orna- 

 mentation, we find that such definitions apply just as truly to one divi- 

 sion as another. Species differ in size and coloration, and also in form, 

 as well as in details of structure, as beautifully exemplified in the 

 groups under consideration. In fact, the difference between species 

 and genera, and genera and orders, are but differences in degree, and re- 

 lative terms; there is nothing absolute in nature. 



Thus the present tendency to sub-divide old genera and admit many 

 new ones, the necessity of establishing new families and sub-families, 

 new orders and sub-orders, must convince the thoughtful observer that 

 the terms classes, orders, etc., now in use are far to few to indicate the 

 manifold sub-divisions, and groups of varying rank and importance ac- 

 tually existing in nature. The attempt to define such unequal divi- 

 sions seems useless, seeing how little equivalent among themselves are, 

 for example, the genera of another. Indeed, the sub-divisions already 



*Agassiz, Essay on Classification, Contributions, Vol. 1, p. 170. 



