REMOVAL OF NASAL PITS AMBLYSTOMA EMBRYOS 33 



relatively limited areas and for concentrated fluids only, and 

 hence the danger of stimulation may be minimized by keeping 

 the source of the stimulus at a distance from the mouth (Herrick 

 '08) and Sherrington ('06). 



The most important sense, then that must be controlled, is 

 the visual. This may be accomplished in two ways, (1) as stated 

 above by keeping the source of the stimulus motionless and (2) 

 by removing the optic vesicles at an early stage. 



In the study of the reactions of Amblystoma to olfactory 

 stimuli, more particularly to the stimulus of food, three sources 

 of stimuli were used, two of which were olfactory and the third 

 purely optic. Pieces of freshly killed Amblystoma larvae and 

 live entomostraca were used to stimulate the olfactory centers; 

 grains of sand, which possess no powers of olfactory stimulus, 

 for the optic centers. 



It was necessary to test as exactly as possible the visual 

 reactions of the larvae since, as is evident to the most casual 

 observer, under ordinary conditions, that sense is the most active 

 in the capture of food. Under normal conditions where the food 

 supply is abundant, individual larvae rarely move about, but 

 remain motionless until a small crustacean comes within strik- 

 ing distance. The reactions of larvae under such conditions are 

 quite characteristic. Resting motionless on the bottom of the 

 aquarium, with body held above the debris and head elevated, 

 it will, with a sudden contraction of the trunk muscles followed 

 by a quick forward lurch, snap and engulf some particular crus- 

 tacean whose movements carry it within striking distance. 



When on the other hand, the supply of moving food is reduced, 

 the larvae will forage the aquarium for food. Under these 

 conditions the reactions are quite as characteristic as in the well 

 stocked aquarium. The young Amblystomas crawl slowly 

 around the aquarium, nosing here and there. The attitude is 

 strikingly like that of a dog following a scent, and suggests that 

 now in the absence of food that is moving, the sense of smell 

 is actively used. Support is given to this suggestion by the fact 

 that the larvae may often be seen to snap up some bit of the 

 debris. 



