THE FUNCTIONS OF LIFE. 45 



frao:ments and interrupted portions of this imagi- 

 nary system : so that, if, for the sake of illustration, 

 we must employ a metaphor, the natural distribu- 

 tion of animals would appear to be represented, not 

 by a chain, but by complicated net- work, where 

 several parallel series are joined by transverse 

 and oblique lines of connexion. A variety of facts, 

 have been adduced in favour of another hypothesis, 

 namely, that the real types or models of structure, 

 are more correctly represented by circular, or re- 

 currincr arrangements.* But as the discussion of 

 these and other topics relating to the plans and 

 designs of nature in the formation of organic beings 

 requires a previous acquaintance with the details 

 of comparative anatomy and physiology, I shall 

 defer all further observations respecting them till I 

 have finished the review I propose to take of the 

 several structures and functions of the animal and 

 vegetable economy. There are, however, some 

 views that have been entertained respecting the 

 procedure of nature in the formation of the diffe- 

 rent races of animals, which it will be proper to 

 notice in this place, as they will occasionally be 

 referred to when the facts that more particularly 

 illustrate and support them come to be noticed. 



An hypothesis has been advanced, that the origi- 

 nal creation of species has been successive, and 

 took place in the order of their relative complexity 

 of structure ; that the standard types have arisen 

 the one from the other; that each succeeding form 

 was an improvement upon the preceding, and fol- 

 lowed in a certain order of developement, according 



* Mr. M'Leay is the author of this circular hypothesis, wliicli 

 he has developed in his " Horce EntomologiccB." 



