KINETOGENESIS. 249 



during its growth and development, that when slight 

 variations in any one part occur, and are accumulated 

 through natural selection, other parts become modi- 

 fied." After referring to various characters of compo- 

 site and unbelliferous plants in illustration of such a 

 law, he says (/. r. , p. 116), "Hence modifications of 

 structure, viewed by systematists as of high value, may 

 be wholly due to the laws of variation and correlation, 

 without being, so far as we can judge, of the slightest 

 service to the species." Here Mr. Darwin admits the 

 insufficiency of natural selection as an explanation of 

 the origin of such characters; for he says (p. iiy), 

 "Natural selection, it should never be forgotten, can 

 act solely for the advantage of each being." He goes 

 further, and admits (p. 114) t;hat the Lamarckian doc- 

 trine has some claims to credence, where he says, "On 

 the whole we may conclude that habit, or use and dis- 

 use, have in some cases, played a considerable part in 

 the modification of the constitution and structure ; but 

 that the effects have often been largely combined with, 

 and sometimes overmastered by the natural selection 

 of innate variations." 



I. KINETOGENESIS OF MUSCLE. 



The fundamental condition of the molar movements 

 of organic beings is the contractility of protoplasm. In 

 the Amoeba this contractility is a generally diffused 

 characteristic of its body-substance, and this is the 

 case with Rhizopoda generally. In higher Protozoa 

 the contractility is already especially developed in cer- 

 tain regions where most needed for the movement of 

 the body in definite directions ; generally immediately 

 beneath the denser sarcode of the external surface. In 



K 



