THEORIES OF LAMARCK AND DARWIN 377 
arise in animals mainly through use and disuse, and new 
organs have the their “origin in a physiological need. A new need 
felt | by the a animal expresses itself on the organism, stimulating 
growth and adaptations in a particular direction. This part 
of Lamarck’s theory has been subjected to much ridicule. 
The sense in which he employs the word besoin has been 
much misunderstood; when, however, we take into ac- 
count that he uses it, not merely as expressing a wish or 
desire on the part of the animal, but as the reflex action 
arising from new conditions, his statement loses its alleged 
grotesqueness and seems to be founded on sound physiology. 
Inheritance.—Lamarck’s view of heredity was uncritical; 
according to his conception, inheritance was a simple, direct 
transmission of those superficial changes that arise in organs 
within the lifetime of an individual owing to use and disuse. _ 
It is on this question c of the direct inheritance of variations 
acquired in the lifetime of an individual that his theory has 
been the most assailed. The belief in the inheritance of 
acquired characteristics has been so so undermined by experi- 
mental evidence that at the present time we can not point 
to a single unchallenged instance of such inheritance. But, 
while Lamarck’s theory has shown weakness on that side, 
his ideas regarding the production of variations have been 
revived and extended. 
Variation.—The more commendable part of his theory 
is the attempt to account for variation. Darwin assumed 
variation, but Lamarck attempted to account_ t for it, and in 
this fe feature_many discerning students maintain that the 
theory of Lamarck is more philosophical in its foundation 
than that of Darwin. . 
In any theory of evolution we must deal with the variation 
of organisms and heredity, and thus we observe that the two 
factors discussed by Lamarck are basal. Although it must 
be admitted that even to-day we know little about either 
