384 Stiidies in the Theory of Descent. 



would occasionally have played other parts, being 

 fashioned once again in these stages into imitations 

 of portions of plants, such as a row of berries or 

 flower-buds. For this, however, there is as yet no 

 positive evidence. 



As the ring-spots became detached from the 

 subdorsal line out of which they had arisen, the 

 latter disappeared more and more completely 

 from the last ontogenetic stage, and receded 

 to wards the younger stages of life of the caterpillar 

 it became historical. This disappearance of the 

 subdorsal may also be explained by the fact that 

 the original longitudinal stripe imitating the linear 

 arrangement of leaves would become meaningless, 

 even if it did not always diminish the effect of the 

 ring-spots. But characters which have become 

 worthless are known in the course of time to 

 become rudimentary, and finally to disappear 

 altogether. I do not believe that disuse alone 

 causes such characters to vanish, although in the 

 case of active organs it may have a large share in 

 this suppression. With markings it cannot, how- 

 ever, be a question of use or disuse nevertheless 

 they gradually disappear as soon as they become 

 meaningless. I consider this to be the effect of 

 the arrest of the controlling action of natural 

 selection upon these characters (suspension of the 

 so-called " conservative adaptation," Seidlitz). 

 Any variations may become of value if the charac- 

 ter concerned is met with in the necessary state of 



