GEOTROPISM IN LARVAE OF TENT CATERPILLAR 



Before 

 eating 



After 

 eating 



When larvae first hatch out of the eggs, they After their first feeding excursion, the larvae 



move up — toward the tips of the twigs, where move down — away from the tips — to a crotch, 



leaf buds are opening. But if the twig is bent where they spin a "tent". But if the twig is bent 



over, they still move up — away from their pro- over, the larvae still move down — toward the tips 



spective food of the bore twigs 



DO THE LARVAE KNOW WHAT THEY ARE DOING? 



The young larvae normally move toward the young leaves when they are hungry 

 and away from the leaf buds when they have filled up on food. But apparently they 

 move up or down under different Internal conditions, even at the risk of going hungry 



— were "reflected" into a muscle. The nature of the force and the actual 

 connection between the stimulus and the response were not worked out for 

 nearly two hundred years. The idea was a helpful one, however, and the 

 term reflex remains in use. 



And we make use of the fact too. For if you ever catch a fish with hook 

 and line, your success depends upon a reflex. The fish responds to the sight 

 of certain kinds of objects by snapping at them with its mouth. If the con- 

 ditions are suitable, if you have the right kind of bait, if it is properly fastened 

 to the hook, and if you drop it into the water at a suitable depth, your "luck" 

 depends upon the presence of the fish and his seeing the bait. The reflex 

 does the rest. This appears to be a mechanical act, like a tropism. We cannot 



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