INSTINCT AND INTELLIGENCE 



or less preparation ; the instinctive part is the impulse 

 that requires the insect to use a certain kind of habi- 

 tation. Any one familiar with T. rubrocinctum would 

 never look for her nest in standing stems or under 

 stones; to use Mr. Morgan's test, he would be willing 

 to bet on the general style of the dwelling-place. All of 

 these acts are similarly performed by individuals of the 

 same sex and race, not in circumstantial detail but quite 

 in the same way in a broad sense. Variation is always 

 present, but the tendency to depart from a certain type 

 is not excessive. In Cerceris the burrow is tortuous, 

 this style of work being common to many species in the 

 genus, and very characteristic. No Sphex nor Ammo- 

 phila constructs any such tunnel. The adherence of 

 all the members of a species to a certain style of archi- 

 tecture is, then, due to instinct. 



The spinning of the cocoon, in those species in which 

 the larva is protected in this manner, and its shape, are 

 instinctive. We find that closely allied species in the 

 same genus make very different cocoons, as is seen in 

 T. rubrocinctum and T. bidentatum. Some wasps spin 

 no such covering for themselves. It is a well-known 

 fact that silkworms sometimes omit the spinning of a 

 cocoon ; but this does not affect the argument, since 

 the descendants of these individuals make the charac- 

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