394 



LAMARCK, HIS LIFE AND WORK 



"The Lamarckian factors (i) change (both direct 

 and indirect) in the milieu, (2) need, and (3) habit, 

 and the now generally adopted principle that a 

 change of function induces change in organs,* and 

 in some or many cases actually induces the hyper- 

 trophy and specialization of what otherwise would 

 be indifferent parts or organs ; — these factors are all- 

 important in the evolution of the colors, ornaments, 

 and outgrowths from the cuticle of caterpillars." 



Our present views as to the relations between the 

 Lamarckian factors and the Darwinian one of nat- 

 ural selection are shown by the following summary 

 at the end of this essay. 



" I. The more prominent tubercles, and spines or 

 bristles arising from them, are hypertrophied pilifer- 

 ous warts, the warts, with the seta or hair which 

 they bear, being common to all caterpillars. 



" 2. The hypertrophy or enlargement was prob- 

 ably [we should rather sd.y possibly] primarily due to 

 a change of station from herbs to trees, involving 

 better air, a more equable temperature, perhaps 

 a different and better food. 



" 3. The enlarged and specialized tubercles devel- 

 oped more rapidly on certain segments than on others, 

 especially the more prominent segments, because 

 the nutritive fluids would tend more freely to supply 

 parts most exposed to external stimuli. 



" 4. The stimuli were in great part due to the 

 visits of insects and birds, resulting in a mimicry of 

 the spines and projections on the trees; the colors 



* E. J. Marey : " Le Transformisme et la Physiologie Experi- 

 mentale, Cours du College de France," Revue Scienti/itjue, 2°"= serie, 

 iv., p. 8l8. (Function makes the organ, especially in the osseous and 

 muscular systems, ) See also A. Dohrn : £>er Ursprung der Wiebel- 

 thiere und das Princip des Functionswechsels, Leipzig, 1875. See 

 also Lamarck's opinion, p. 295. 



