THE RELATION OF LIFE TO OTHER FORCES. 715 



there is but one parent; and this hermaphrodite-form of generation is 

 the rule in the vegetable and least developed portion of the animal king- 

 dom. At last, in all animals but the lowest, and in some plants, the 

 portions of organized structure specialized for development after their 

 mutual union into a new individual, are found on two distinct beings, 

 which we call respectively male and female. 



The old idea concerning the power of growth resident in the germ of 

 the new being, thus formed in various ways, was expressed by saying 

 that a store of dormant vitality was laid up in it, and that so long as no 

 decomposition ensued, this was capable of manifesting itself and becom- 

 ing active under the influence of certain external conditions. Thus, the 

 dormant force supposed to be present in the seed or the egg was assumed 

 to be the primary agent in effecting development and growth, and to 

 continue in action during the whole term of life of the living being, ani- 

 mal or vegetable, in which it was said to reside. The influence of exter- 

 nal forces heat, light, and others was noticed and appreciated; but 

 these were thought to have no other connection with vital force than 

 that in some way or other they called it into action, and that to some 

 extent it was dependent on them for its continuance. They were not 

 supposed to be correlated with it in any other sense than this. 



Now, however, we are obliged to modify considerably our notions and 

 with them our terms of expression, when describing the origin and birth 

 of a new being. 



To take, as before, the simplest case a seed or egg. We must sup- 

 pose that the heat, which in conjunction with moisture is necessary for 

 the development of those changes which issue in the growth of a new 

 plant or animal, is not simply an agent which so stimulates the dormant 

 vitality in the seed or egg as to make it cause growth, but it is a force, 

 which is itself transformed into chemical and vital power. Tho embryo 

 in the seed or egg is a part which can transform heat into vital force, 

 this term being a convenient one wherewith to express the power which 

 particular structures possess of growing, developing, and performing 

 other actions which we call vital. 1 Of course the embryo can grow only 

 by taking up fresh material, and incorporating it with its own structure, 

 and therefore it is surrounded in the seed or ovum with matter sufficient 

 for nutrition until it can obtain fresh supplies from without. The ab- 

 sorption of this nutrient matter involves an expenditure of force of some 

 kind or other, inasmuch as it implies the raising of simple to more com- 

 plicated forms. Hence the necessity for heat or some other power before 



1 The term " vital force " is here employed for the sake of brevity. Whether it is 

 strictly admissible will be discussed hereafter. 



The general term force is used as synonymous with what is now often termed 

 energy. 



