440 UNITY OF DESIGN. 



development of elements, which existed in a latent form in 

 the primeval germ, and which are evolved, in succession, 

 as nature advances in her course. Thus, we find that each 

 new form which arises, in following the ascending scale of 

 creation, retains a strong affinity to that which had preceded 

 it, and also tends to impress its own features on those which 

 immediately succeed; and thus their specific differences re- 

 sult merely from the different extent and direction given to 

 these organic developments; those of inferior races proceed- 

 ing to a certain point only, and there stopping; while in be- 

 ings of a higher rank they advance farther, and lead to all 

 the observed diversities of conformation and endowments. 



It is remarked, in farther corroboration of thes^ views, 

 that the animals which occupy the highest stations in each 

 series possess, at the commencement of their existence, forms 

 exhibiting a marked resemblance to those presented in the 

 permanent condition of the lowest animals in the same se- 

 ries; and that, during the progress of their development, 

 they assume, in succession, the characters of each tribe, cor- 

 responding to their consecutive order in the ascending chain: 

 so that the peculiarities which distinguish the higher ani- 

 mal, on its attaining its ultimate and permanent form, are 

 those which it had received in its last stage of embryonic 

 evolution. Another consequence of this hypothesis is that 

 we may expect occasionally to meet, in inferior animals, with 

 rudimental organs, which from their imperfect development 

 may be of little or no use to the individual, but which be- 

 come available to some superior species, in which they are 

 sufficiently perfected. The following are among the most 

 remarkable facts in illustration of these propositions. 



In the series of Articulated Animals, of which the An- 

 nelida constitute the lowest, and winged Insects the highest 

 terms, we find that the larvae of the latter are often scarcely 

 distinguishable, either in outward form, or in internal or- 

 ganization, from Vermes of the lower orders; both being 

 equally destitute of, or but imperfectly provided with ex- 

 ternal instruments of locomotion j both having a distinct vas- 



