ADAPTATIONS OP SUKVIVAL VALIK 



dead tadpoles in thirty-five minutes of continuous observation and at the 

 end of this time all were like the controls in behavior. However, eventually 

 the tadpoles in this dish, which was left undisturbed, fed readily on the mud 

 and the dead tadpoles disappeared in several days. All ten eventually trans- 

 formed with no tendency toward cannibalism at any time. 



One other observation should be noted. Whenever the thermometer was 

 lowered into any of these dishes, some tadpoles invariably came to nibble 

 briefly at the bulb as though finding it by sight and testing it as a possible 

 food source. 



It was concluded that (1) the substances in the bouillon cube in the con- 

 centrations and proportions used elicited a negative reaction from the tad- 

 poles (a wholly unexpected result); (2) the raisin caused a reaction which 

 was at first only weakly positive; however, it later became stronger; (3) bot- 

 tom mud with dead tadpoles in it elicits a weak positive response, or none 

 at all, at first but later serves as a satisfactory food source; (4) whether food 

 materials are found by response to chemicals or not, sight plays a part in "in- 

 vestigation" of possible food sources. 



An observation made in the laboratory concerned the tadpoles' reaction 

 to a larger animal. A juvenile Scaphiopus bombifrons in the Biological Sur- 

 vey laboratory was noted to be in need of water. As a quick source, it was 

 placed into a culture of S. hurtcrii tadpoles. Immediately it was attacked 

 by hundreds of tadpoles, which swarmed about it nibbling at all its sub- 

 merged parts. The little spadefoot was too large to be harmed, but it acted 

 as though annoyed, brushing tadpoles away with its front legs and occasion- 

 ally changing its position. This shows that S. hurtcni tadpoles, if hungry, 

 may attack quite large living vertebrates and recalls the attack on my finger 

 at Pool D. 



A further series of observations bear upon the same method of behavior. 

 A large mass of tadpoles had been transferred from Pool D to my home and 

 placed in clear water in the small artificial pool mentioned in a recent paper 

 (Bragg, 1948). Here they behaved typically, including schooling and forma- 

 tion of feeding aggregations till they underwent metamorphosis. 



About two hours after first placing these tadpoles into the pool, I held 

 a small mass of ground beef (about % inch in diameter) in the water near 

 feeding tadpoles. None at first paid it any attention. After about three inin- 

 utes, a tadpole swimming at random and obviously not attracted, blundered 

 into it and immediately began feeding voraciously. I dropped the meat to 

 the bottom of the pool and watched the behavior of the tadpoles closely for 

 the next half hour and at intervals thereafter. At first only a few found it, 

 but soon it was covered by a dense mass of agitated tadpoles. All evidence 

 of it had disappeared late that night except a few pieces of fatty tissue floating 

 on the surface. The most interesting thing observed was that the response 

 seemed to be more to sight than to chemical diffusion from the food. I had 

 a very definite impression that when one tadpole finds a food object others 

 note it and come; the more tadpoles that accumulate, the greater the stimu- 

 lation so that a great mass is thus built up. This simple observation, therefore, 



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