THE LAMARCKIAN THEORY 243 



other hand, the continued lack of use of the same organ 

 sensibly weakens it; it deteriorates, and its faculties 

 diminish progressively until at last it disappears." 



Those modifications, however, would not have any 

 importance as far as the future of the species is con- 

 cerned unless they were transmitted to the following 

 generations. Their hereditary character is affirmed 

 by Lamarck's second law: "Nature preserves every- 

 thing that she has caused the individual to acquire or 

 lose by the influence of the circumstances to which the ■ 

 race has been for a long time exposed, and conse- 

 quently by the influence of the predominant use of 

 certain organs (or in consequence of its continued dis- 

 use). She does this by the generation of new indi- 

 viduals which are produced with the newly acquired 

 organs. This occurs, provided that the acquired 

 changes were common to the two sexes, or to the indi- 

 viduals that produced the new forms." 8 



The physiological information at hand in La- 

 marck's days did not enable him in the least to explain 

 how the phenomena mentioned in these two laws can 

 be brought about, how organs develop by use and how 

 acquired characters are transmitted hereditarily. «• 

 And very naturally, he gives us explanations which 

 were considered as such in his time. This defect is 

 particularly noticeable in the second volume of "Philo- 



8 Vol. I, pp. 335-236. 



