TRACHEATES 2 I 3 



course of an individual life certainly strengthens an 



organ, though the result of it is not, in my opinion, 



inherited. As the antlers of a stag need years to grow, 



and their weight does not increase so very much in 



each year, the head and neck will become stronger 



under their increasing burden, so that an old sixteen- 



pointer can bear a considerable weight. However, 



this strengthening by use can only advance to a certain 



point, as we see in the old illustration of the man who 



carried a calf every day and so was able to lift it even 



when it had grown into an ox. The man could never 



have lifted two oxen, even if he had begun with two 



calves. Hence there came a time in the development 



of the giant stag when the antlers were so heavy as to 



interfere with the mobility of the animals ; then the 



animals were selected which had a stronger constitution 



from birth. 



Hence, as the co-adaptations do not need to appear 



simultaneously, but may be selected successively during 



long periods, they present no difficulty to natural 



selection. The Lamarckian principle is not only 



inapplicable to a number of co-adaptations, but it 



is wholly unnecessary for explaining harmonious 



adaptations.^ 



1 Weismann further instances the many co-adaptations of the ant 

 and bee-workers, whose frame cannot have been formed by the 

 inheritance of the effects of use, because the workers inherit nothing, 

 since they do not reproduce at all. The queens, which give birth to 

 the workers along with the rest, have a totally different structure. 

 Weismann explains the case by a selection of stocks. Those stocks were 

 always preserved, the workers of which took most care of the eggs and 

 the stock. At the same time those queens were selected which were not 

 only the best queens, but also brought the best workers into the world. 



