86 GENERAL ZOOLOGY 



its egg-shell would therefore be called instinctive, as would 

 the behavior of Pronuba in pollinating the yucca. 



Dr. and Mrs. Peckham, in their work, The Solitary Wdsps, 

 from which we have quoted before, enumerate eight primary 

 instincts : 



1. Stinging. 



2. Taking a particular kind of food. 



3. Method of attacking and capturing prey. 



4. Method of carrying prey. 



5. Preparing nest and capturing prey, or the reverse. 



6. The mode of taking prey into the nest. 



7. The general style or locality of nest. 



8. The spinning or not spinning of a cocoon, and its specific form 

 when made. 



Some instincts seem to be little more than direct responses 

 of the nervous system of the animal to external exciting 

 causes (see paragraph 011 reflex action, Chapter XVI, p. 208). 

 Thus it is well known that moths and some other night-flying 

 insects show a positive reaction toward light, which, under 

 certain conditions, may tend toward the destruction of the 

 insects, as may be seen about electric arc-lights in city parks 

 in summer. The blow-fly is attracted to the decaying meat 

 in which it lays its eggs by the chemical substances given 

 off, which are perceived by the fly's sense of smell. Experi- 

 ments on certain caterpillars seem to show that their life is 

 largely determined by their positive reaction to light, their 

 negative reaction to gravity, these two combining to compel 

 the caterpillars to crawl upward, and a contact reaction 

 with the convex terminal buds, tending to hold the cater- 

 pillar in place when at the end of twigs. When branches 

 were inverted and placed in a receptacle in which certain 

 caterpillars were, the latter remained at the top of the twigs, 

 though food was only a few inches away, showing that the 

 caterpillars were not normally attracted to their feeding-place 

 at the ends of twigs merely by the presence of food there. 



