66o THE POPULAR SCIENCE MONTHLY. 



whicli have gradually grown up in my mind. Others, I observe, per- 

 haps nearly all evolutionists, are tljinking in much the same direction, 

 but I have not yet seen any distinct presentation of the subject. 



The movements of the animal body, you will remember, are divided 

 into two great groups, the voluntary and the involuntary or reflex. 

 Bui between these extremes there are undoubtedly many intermediate 

 terms connecting them. Thus is it in all our science, and still more 

 in our systematic teaching of science. Our distinctions are far more 

 trenchant than the distinctions in Nature. It must and ought to be 

 so, for we must get firm hold of the types first, and then we are pre- 

 pared to study the intermediate gradations. Of the intermediate 

 terms in this case there are two which are quite distinct. Including 

 the extremes, therefore, we have four kinds of animal movements: 



1. The perfect voluntary movements. These require the full, con- 

 stant, and immediate exercise of the will ; and, when the movement 

 is complex, requiring in addition the whole thought and attention 

 fixed, often painfully fixed, on the movement. In this category are 

 nearly all movements when accomplished for the first time. 



2. Hahitual movements. These are semi-volitional. They are 

 removed from thoughtful attention, from immediate and painful effort 

 of tlie will. A general superintendence only of the will is necessary. 

 When any thing goes wrong the mind takes cognizance and corrects 

 it by direct act of the will, and the movement falls, for the time being, 

 into the first category; but otherwise the thoughts and attention may 

 be directed to something else. These are, therefore, to some extent, 

 automatic. Such are, in man at least, the moA^ements in walking, fly- 

 ing, swimming, speaking, playing on a musical instrument, etc. These 

 were, in all cases, at first movements of the first kind, but fell into the 

 second ca,X,Qgoxj hy repetitio7i. They are ac2^^^Ve<^, therefore, wholly 

 by individual experience. 



3. Instinctive movements or acts. These are still fartlier re- 

 moved from the category of the first group. They are removed, not 

 only from thoughtful attention, but also from, indvidual experience. 

 If we compare them with habitual acts, they are hiherited habits. 

 They are evidently the result of inherited hrain-structure, but they 

 are not yet wholly removed from the sphere of consciousness and will. 

 Such are the actions of bees and other insects already described. 



4. Lastly, Reflex movements. These are wholly automatic. They 

 afe wholly removed not only from thoughtful attention and individual 

 experience, but also from consciousness and will. Tliese are therefore 

 the extreme type of movements determined with the greatest pre- 

 cision by inherited structure of the nervous centres. Such are the 

 movements of the heart, the stomach, the intestines, etc. 



Now, of these four kinds of acts, 1 and 2 and 3 are evidently formed 

 the one from another, i. e., 2 from 1 and 3 from 2. The fourth I can- 

 not account for in a similar way, for it must have preceded all the 



