508 DEVELOPMENT OF THE SPECIAL FROM THE GENERAL. 



ored to do, the animal tribes with ourselves ; of measuring their instincts 

 with our mental operations ; things which are different terms of two dif- 

 ferent series, and things which are incommensurable. 



There are three cases in which we might consider this career. These 

 are, first, in the development of particular organs, as the digestive, res- 

 piratory, or circulatory ; second, in the development of individual beings, 

 which pass in their onward progress, as we have said, through various 

 forms in succession; third, in the development of species, presenting 

 what have been formerly designated as successive stages of increasing 

 perfection. For all these various cases a single illustration may suffice, 

 illustration of Thus, in the primitive period of life, a single membrane dis- 

 the unfolding charges promiscuously and contemporaneously all the va- 



of the special f . f ,. ., -,. . .. . . 



from the gen- nous organic functions it digests, it respires, it secretes ; 

 eral - but, a little .advance onward, special portions of it are allot- 



ted for one and another of these uses, and a localization, a centralization 

 of function ensues, and things that were mixed in confusion become sep- 

 arate and distinct. As the passage onward is made, still farther special- 

 izations are introduced, and so on in succession. Thus at the two ex- 

 tremes we may contemplate the single germinal membrane of the ovum, 

 which is discharging contemporaneously every function digesting, ab- 

 sorbing, respiring, etc. and the complete organic apparatus of man, the 

 stQmach, the lungs, the skin, the kidneys, and the liver mechanisms 

 set apart each for the discharge of a special duty, yet each having arisen, 

 as we know positively from watching their order of development, from 

 that simple germinal membrane. We must not, therefore, permit our- 

 selves to be deceived by the appearance of complexity they exhibit, 

 since, intricate as may be their construction, they have all arisen through 

 gradual centralization, one duty being separated from another, and hav- 

 ing an appropriate mechanism for itself; and so, at last, it comes to pass 

 that even the minutest conditions are discharged by a special part. 

 Thus, in the kidney, the salts are removed by one portion of the struc- 

 ture and the organic constituents by another ; yet, even in these ut- 

 most conditions of refinement, the primitive condition is at all times 

 ready to be reproduced, and, when driven to it, each of these structures 

 can act vicariously for the others, and discharge for the others their 

 duty. 



It is unnecessary for our purpose to multiply instances, since every 

 page of natural history, comparative anatomy, and embryology presents 

 them in abundance ; but it may be to the purpose to remark that this 

 doctrine leads to more worthy conceptions of the system of nature ; 

 for if we suppose that there has been, in the case of the animal series, 

 a passage from things that are less perfect to things that are more so, 

 though this may be agreeable to our own experience, which is essen- 



