THE ENERGY OF LIFE EVOLUTION. 



795 



less entire ; and the ossification of its sheath and substance is laid 

 down in the three segments already described. 



The two segments visible from one side of the column form two 

 wedges with their apices together, and their bases one up and the 

 other down. Now, if a person who wears a coat of rather thick mate- 

 rial will examine the folds of his sleeve as they are produced on the 

 inner side of his arm, he will see a figure nearly like that of the seg- 

 ments of the vertebral column described. The folds will correspond 

 to the sutures, and the interspaces to the bony segments. He will find 

 that the spaces are lens-shaped, or, when viewed in profile, wedge- 

 shaped, with the apices together. This arrangement results from the 

 necessary mechanics of flexure to one side. In flexure of a cylinder 

 like the sleeve, or like a vertebral column, the shortest curve is along 

 the line of the greatest convexity of the cylinder. Here is the closest 

 folding of the sheath, and here, consequently, the lines of fold in soft 

 material, or fracture in hard material, will converge and come to- 

 gether. That is just what they do in both the sleeve and the rhachi- 

 tomous vertebral column, the only difference being that in the animal 



Fig. 6. The Folds on the Inner Side op a Coat-sleeve, which correspond with the lines 

 separating the segments of the vertebrae of the Eryops. The letter i is the basal segment or 

 intercentrum ; the p corresponds with the lateral segment, the pleurocentrum ; and n repre- 

 sents the basal part at the upper or neural arch, which rests on p and i. 



it is exhibited on both sides, and on the sleeve on only one side. This 

 difference is, of course, due to the fact that the animal can bend him- 

 self in both directions, while the arm only bends in one direction. 



It results from the above observations that the structure of the 

 rhachitomous vertebral column has been produced by the movements 

 of the body from side to side, as in swimming, during the process of 

 the deposit of mineral material in and around the chorda dorsalis.* 

 Here we have another convincing proof that use and effort have pro- 

 duced animal structure. 



Instances like the above can be cited from many departments of 

 zoology wherever paleontology has pointed out the lines of descent. 

 I will not cite them further, but will draw some conclusions which are 

 necessary and which are of general. interest. 



It is evident that use and effort imply some kind of movement on 

 the part of the animal which puts them forth. Hence I have called 



* This subject is more fully treated of in the " American Naturalist " for January, 

 1884. 



