INSTINCT AND FINAL TENDENCY. 27 



lacking in firmness and could not be closed so tightly 

 as it should be. 



But if, as is actually the fact, our architect chooses 

 to make the concave part of the margin longer in the 

 above mentioned proportion to the leaf's outer mar- 

 gin, then all requirements are most admirably met, 

 and not a trace of the disadvantages of the former 

 methods can be discovered. Without wishing to main- 

 tain that no other curve might possibly bring about 

 the same result, there is certainly none so simple and 

 yet so wonderfully appropiate. 



To understand this still more clearty, we may finally 

 direct our attention for a moment to the purpose 

 which the funnel has. What is the real destiny of this 

 artistic house? To insure the preservation of the 

 species of Rhynchites betulce, it is absolutely necessary 

 that in its larval stage the young progeny should be 

 guarded against all harmful influences resulting from 

 atmospheric changes. Now it has been experimentally 

 proved that every larva, in spite of abundant v food, 

 simply dries up when taken out of the tightly rolled 

 and well-sealed funnel. Moreover, on account of the 

 constitution of its stomach , the larva can feed only on 

 dry leaves, supplied by its habitation. That the birch 

 leaf might be dry in due time, the mother beetle 

 wisely provided by making the incision in the 

 leaf's central rib. Finally, because the number of its 

 progeny is so exceedingly small, it had to guard them 

 well against all insectivorous animals. But who can 

 suggest a hiding-place better adapted to its purposes 

 than a dry, meaningless leaf, rolled up and closed with 

 so great care? 



