Differentiation. 269 



plasm. Contraction of muscle is tiro result in general of electrical 

 stimulus, and the necessary amount of electrical energy for the purpose 

 of this contraction may be generated by any one of several other forms 

 of energy, such as light, heat, or touch, or pressure by another body> 

 when such forms of energy are applied to the muscle. Further on we 

 shall see how these various forms of energy are interconvertible into 

 each other, but here it is enough to state that the structure of muscular 

 protoplasm, if not of all protoplasm, is of sufficient sensibility to be af- 

 fected by the electrical energy generated by even a touch, a ray of 

 light, a beam of heat, or a sudden compression of the air or vibration 

 of the water in which it may happen to be. Even vegetable protoplasm 

 is contractile under electrical stimulus. 



Now, in the Moneron the differentiation of parts has not gone far 

 enough to exempt any of its protoplasm from this contractility ; any 

 part stimulated will act as a muscle, contracting at one point and 

 thereby necessarily pushing out at another. In one sense, therefore, 

 the whole animal is a muscle. A particle of foreign matter suitable for 

 its food, coming adventitiously into contact with it, excites a different 

 sort of reaction. In the process of muscular contraction certain mole- 

 cules composing the organism have become disrupted by the tearing out 

 of the carbon atoms. The elements about the voids thus left remain 

 with unsaturated affinities, or, in other words, are hungry. They are 

 therefore all impelled alike towards such accidental atoms of carbon as 

 are available for new combinations, and so the" food is surrounded, and 

 the animal, after first becoming all mouth, is next, for the time being, 

 all stomach. The atoms suitable for assimilation being extracted from 

 the food particle, the several elements of the animal shrink from the 

 unassimilable remains of the repast, and so, by their common movement, 

 an act of excretion is accomplished. Respiration is a process by which 

 ox} T gen from the air is brought into contact with the atoms of carbon in 

 the tissues of the animal. Without it no sort of animal movement can 

 take place. In the Moneron each molecule of its protoplasm must come 

 into direct contact with the air and so allow the oxidation of its carbon. 

 Probably intermolecular movements of the protoplasm alternately bring 

 the interior molecules to the surface. So the lungs of the animal may 

 be said to be coextensive with its body. It is all lungs. According to 

 the statement above, that external stimuli arrested by the tissues of the 

 animal are converted into quasi electrical vibrations, it follows that these 

 vibrations must traverse the mass passing from one molecule to another; 

 from those more exposed to the direct influence of the stimuli, to those 

 less exposed. For in even a Moneron we are bound to suppose top, , 

 bottom and sides, even though the parts are continually exchanging po- 

 sitions. Each molecule is therefore to be considered a vehicle for the 



