ANATOMY AND PHYSIOLOGY OF THE HORSE. 



129 



this class are remarkable for the immense 

 number of eggs which most of them pro- 

 duce, for the metamorphoses which many 

 of them are known to undergo, and for the 

 varieties of form under which there is reason 

 to suspect that the same germs may de- 

 velop themselves, it becomes obvious that 

 no adequate proof has yet been afforded 

 that they have been, in any particular case, 

 otherwise than the products of a pre-existing 

 living organism. This, again, is the con- 

 clusion to which all the most general doc- 

 trines of Physiology necessarily conduct us. 

 For it is most certain that we know noth- 

 ing of Vital Force, save as manifested 

 through organized structures ; whilst, on the 

 other hand, the combination of inorganic 

 matter into organized structures is one of 

 the most characteristic operations of vital 

 force ; hence it is scarcely conceivable that 

 any operation of physical forces upon inor- 

 ganic matter should evolve a living organ- 

 ism. Nor is such a conception more feasi- 

 ble, if it be admitted that vital force stands 

 in such a relation to the physical forces, 

 that we may regard the former as a mani- 

 festation of the latter, when acting through 

 organized structures ; since no vital force 

 can be manifested (according to this view), 

 and no organization can take place, except 

 through a pre-existing organism. 



" It may be further considered as an es- 

 tablished physiological truth, that, when 

 placed under circumstances favorable to 

 its complete evolution, every germ will de- 

 velop itself into the likeness of its parent; 

 drawing into itself, and appropriating by 

 its own assimilative and formative opera- 

 tions, the nutrient materials supplied to it ; 

 and repeating the entire series of phases 

 through which its parent may have passed, 

 however multiform these may be.* Now 

 the germs of all tribes of plants and 

 animals whatever bear an extremely close 

 relation to each other in their earliest con- 

 dition ; so that there is no appreciable dis- 



* The apparent exceptions to this rule, which have heen 

 brought together under the collective term, " Alternation of 

 Generations," will be presently considered, and will be 

 shown to be only exceptional when misinterpreted. 

 17 



tinction amongst them, which would enable 

 it to be determined whether a particular 

 molecule is the germ of a Conferva or of 

 an Oak, of a Zoophyte or of a Man. But 

 let each be placed in the conditions it re- 

 quires ; and a. gradual evolution of the 

 germ into a complex fabric will take place, 

 the more general characters of the new or- 

 ganism preceding the more special^ as 

 aheady explained. These conditions are 

 not different in kind from those which are 

 essential to the process of nutrition in the 

 adult ; for they consist, on the one hand, in 

 a due supply of aliment in the condition 

 in which it can be appropriated; and, on 

 the other hand, in the operation of certain 

 external agencies, especially heat, which 

 seems to supply the force requisite for the 

 developmental process. Now, although we 

 may not be able to discern any such osten- 

 sible differences in the germs of different 

 orders of living beings as can enable us to 

 discriminate them from each other, yet, see- 

 ing so marked a diversity in their operations 

 under circumstances essentially the same, 

 we cannot do otherwise than attribute to 

 them distinct properties ; and it will be con- 

 venient to adopt the phrase germinal capa- 

 city as a comprehensive expression of that 

 peculiar endowment, in virtue of which 

 each gerii. Jevelopes itself into a structure 

 of its own specific type, when the requisite 

 forces are brought to bear upon it, and the 

 requisite materials are supplied to it.* 

 Thus, then, every act of development 

 may be considered as due to the force sup- 

 plied by heat or some other physical agency, 

 which, operating through the organic germ, 

 exerts itself as formative power ; whilst the 

 mode in which it takes effect is dependent 



* This tenn is preferred to that of " germ-power " sug- 

 gested by Mr. Paget, because the latter seems to imply 

 that the force of development exists in the germ itself. 

 Now, if this were true, not only must the whole formative 

 power of the adult have been possessed by its first cell- 

 germ, but the whole formative power of all the beings 

 simultaneously belonging to any one race, must have been 

 concentrated in the first cell-germ of their original proge- 

 nitor. This seems a reductio ad absurdum of any such 

 doctrine ; and we are driven back on the assumption 

 (which all observation confirms), that the /ore* of develop- 

 ment is derived from external agencies. 



