TRACHEATES 2O7 



have arisen by use and the inheritance of its results, 

 The whole coat, with all these prominences, is a 

 dead structure ; it can only be worn out by use, as it 

 has no living parts to replace or increase what has been 

 used up. The animals retain this shell until they die ; 

 no new one is formed underneath it, and there is no 

 coat-producing skin there to be influenced by pressure 

 or use. Hence the peculiarities of the imago coat of 

 these insects cannot possibly be explained by the 

 Lamarckian principle. 



But they are explained by natural selection. Every 

 living thing varies, and so there will be a slightly 

 different imago formed under the pupa-cover of each 

 separate insect. When the animals issue forth, their 

 variations come to light, and are selected or rejected 

 according as they are useful or otherwise. They will 

 either be preserved and accentuated by continuous 

 selection, or they will disappear. And as the 

 Lamarckian principle cannot possibly have formed 

 the details of the coat of these insects, but natural 

 selection may have done so, we have a right to assume 

 that the shell of the Crustacea and of the insects with 

 gradual growth was not brought about by the " inheri- 

 tance of functional modifications," but by a process of 

 selection. 



There are certain adaptations which many experts 

 think cannot be explained by natural selection, but only 

 by the Lamarckian principle. These are what are 

 known as " harmonious adaptations " or co-adaptations. 



There were in former ages stags with antlers six and 

 a half yards high. The animals could, of course, only 



