362 I)r Barry on the Unity of Structure 



general direction in the several sections, with various particular 

 directions, according to various particular and proper functions, 

 in their subdivisions. 



It appears, then, that unity of plan, which we have seen to 

 direct general structure in the animal kingdom as a whole, ex- 

 tends to the general structure of an individual organism. Thus 

 particular organs originating in the same lamina of the germinal 

 membrane or tube, of the same organism, may perhaps be com- 

 pared to individuals of different sexes in the same species. 



A great deal of labour seems to have been lost, in endeavour- 

 ing to find out corresponding parts, as well in different organ- 

 isms as in the same organism, because directed to the examina- 

 tion of perfect structures. How much of this labour, perhaps, 

 too, some octavos, might have been spared, had due regard 

 been paid to the fundamental similarity in structure, and to the 

 identity that exists in the manner of development, of two germi- 

 nal membranes. To a few general and easily understood prin- 

 ciples, are referable all analogies, whether in the same organism, 

 or in different organisms, as well as all congenital anomalies. 



The same remarks are applicable to Classification ; which, as 

 already said,* can have no sure basis in structure, as met with 

 in the perfect state; when different functions, performed by cor- 

 responding parts of structure, tend to embarrass and mislead. 

 Nomenclature also, depending thus on data that are uncertain, 

 must be fraught with error. 



The fact is, that naturalists have begun, just where they 

 should have ended. They have attended to details, but neglect- 

 ed general principles. Instead of analyzing, their process has 

 been one of synthesis. Their attention has been directed to the 

 grouping of the twigs, as if thus they were to find their natu- 

 ral connections, without even looking for assistance towards the 

 branches, or the trunk that gave them forth. But the simile is 

 inadequate ; the labour lost, has been greater than even this sup- 

 poses. For in the grown tree of animal structure, parts, once 

 essentially the same, not only have diverged in their develop- 

 ment, and become elaborated into very different forms, but, as 



Page 136 of the last Number of this Journal. 



