79 6 THE POPULAR SCIENCE MONTHLY. 



the theory which holds that the structures of animals are the results of 

 their movements the theory of kinetogenesis (from kineo, I move, and 

 genesis). This theory is supported not only by the class of facts 

 which I have adduced, but by another large class of a different kind, 

 which demonstrate the alternative proposition, viz., that disuse is fol- 

 lowed by loss and extinction of parts. This may be inferred from the 

 very degenerate character of most animal parasites taken in connec- 

 tion with their embryology. The absence of limbs, of segments, of 

 sense-organs, and even of more important vital organs observed in 

 various parasites, is very remarkable. It is equally remarkable that 

 the history of the development of such animals shows that in their 

 earlier stages they are not parasitic, and possess many organs which 

 are wanting in the adult. This brief history, condensed into the life 

 of each individual parasite, no doubt, as in all growth-history, merely 

 repeats that of the species as a whole. It teaches us that the ances- 

 tors were active, independent swimmers or fliers, as the case may have 

 been, and that by the adoption of parasitic habits they ceased to use 

 the many parts, which consequently dwindled and disappeared. This 

 conclusion is sustained by paleontology wherever evidence can be ob- 

 tained from that source. This is most evident in the history of the 

 reptiles. Many forms of lizards of the present period are known to 

 display curious defects. Such are the absence of some or all of the 

 toes ; of some or all of the limbs ; of the eyelids ; of the dermal folds 

 about the eyes ; and, finally, of the eyes themselves. Paleontology 

 shows that these are not ancient or primitive types which survived, 

 but that they are modern. Now, nearly all such lizards have habits 

 which involve the least possible use of the limbs and of the sense of 

 sight ; they are subterranean, and many of them inhabit ants' nests 

 and devour those insects for food. It is evident that here is a kind of 

 parasitism, and its consequences are of the most marked character. 



The nature of animal movements may now claim our attention. 

 These, we know, are referred to two general divisions, the automatic 

 and the voluntary. The popular definition of these classes of move- 

 ments is that, in the latter case, choice or preference, and therefore 

 will, is supposed to be exercised, and that in the former there is no 

 such quality displayed. The automatic movements are called mechani- 

 cal, and may be performed unconsciously, as the movements of the 

 heart and digestive system, etc. Rigorously, however, the so-called 

 voluntary acts do not proceed from any freedom or will proper on the 

 part of an animal. They appear to do so, because they display intel- 

 ligence of a higher order than the automatic acts, although it is true 

 that intelligent design is not wanting from the latter either. More- 

 over, the so-called voluntary acts may be unconsciously performed, and 

 the automatic may be consciously performed, as in the winking of the 

 eyes and breathing, when attention is directed to them. So, then, the 

 classification into conscious and unconscious is quite independent of that 



