9 



eiice ill faculty between the lowest plant and tlie highest, or be- 

 tween plants and animals. But the difference between the pow- 

 ers of the lowest plant, or animal, and those of the highest is 

 one of degree, not of kind, and dejjends, as Milne-Edwards long 

 ago so well pointed out, upon the extent to which the principle 

 of the division of labor is carried out in the livhig economy. In 

 the lowest organism all parts are competent to perform all func- 

 tions, and one and the same portion of protoplasm may succes- 

 sively take on the function of feeding, moving, or reproducing 

 apparatus. In the highest, on the contrary, a great number of 

 parts combine to perform each function, each part doing its allot- 

 ted share of the work with great accuracy and efficiency, but 

 being useless for any other purpose. On the other hand, not- 

 withstanding all the fundamental resemblances which exist be- 

 tween the powers of the protoplasm in plants and in animals, 

 they present a striking difference (to which I shall advert more 

 at length presently,) in the fact that plants can manufacture fresh 

 protoplasm out of mineral compounds, whereas animals are 

 obliged to procure it ready made, and hence, in the long run, de- 

 pend upon plants. Upon what condition this difference in the 

 powers of the two great divisions of the world of life depends 

 nothing is at present known. 



With such qualification as arises out of the last-mentioned 

 fact, it may be truly said that the acts of all living things are 

 fundamentally one. Is any such unity predicable of their forms? 

 Let us seek in easily verified facts for a rejjly to this question. 

 If a drop of blood be drawn by pricking one's finger, and viewed 

 with proper precautions and under a sufficiently high microscopic 

 power, tliere will be seen, among the innumerable multitude of 

 little, circular, discoidal bodies, or corpuscles, which float in it 

 and give it its color, a comparatively small number of colorless 

 corpuscles, of somewhat larger size and very irregular shape. If 

 the drop of blood be kept at the temperature of the body, these 

 colorless corpuscles will be seen to exhibit a marvelous activity, 

 changing their forms with great rapidity, drawing in and thrust- 

 ing out prolongations of their substance, and creeping about as 

 if they were independent organisms. The substance which is 

 thus active is a mass of protoplasm, and its activity differs in de- 

 tail, rather than in principle, from that of the protoplasm of the 

 nettle. Under sundry circumstances the corpuscle dies and be- 

 comes distended into a round mass, in the midst of which is seen 



