TRACHEATES 2 1 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 



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. 



