Morphological J'ariatioii and Its Causes in A. tigrinuin 65 



dinary larvae are rather slow in taking food from the bottom — 

 earthworms, meat, or insect larvae. They react mainly to tactile 

 stimuli, although strong odor (taste?) sets them to slowly back- 

 ing up and rooting about with the muzzle, finally snapping in 

 case a moving object touches the jaws. About their manner 

 of taking free-swimming prey, daphnids, water-boatmen, etc., 

 there is also nothing striking except under such circumstances 

 as I have described. The organisms are snapped up either when 

 they touch the jaws or when they come into suitable range of 

 vision. Larvae fed from the forceps do frequently learn to see 

 the meat coming, and rise a little distance for it. Some of them 

 even recognize the approach of a person several feet away. But 

 with baby cannibals the capture of living food has evidently been 

 a much more stimulating experience, and the sight of moving 

 prey at a distance of several inches excites them strongly. I 

 placed several young cannibals, hardly more than 6 cm. long, in 

 large battery jars of clear water. One at a time I introduced 

 some nearly grown tadpoles of Chorophilus. These latter are 

 especially active, and even when not swimming are incessantly 

 vibrating their tails. Such tail-wagglings were more than the 

 calmest young broad-head could stand. Some started in imme- 

 diate pursuit, though approaching cautiously for the final grab. 

 Others, however, when a Chorophilus chanced within their dis- 

 tant range of vision, across the bottom of the jar, went through 

 the most astonishing mimicry of the behavior of a larger car- 

 nivore. First, the animal rose -slightly on its limbs, swaying for- 

 ward ; then a forward stride or two, then a pause, followed by an- 

 other slow forward movement. If at this stage the Chorophilus 

 again vibrated its tail, as it was most likely to do, an actual 

 tremor could plainly be seen to pass over the body of the canni- 

 bal, and it again slid forward more rapidly. So closely did this 

 whole process simulate the movements of a cat stalking a bird, it 

 seemed impossible to believe the movements observed were but 

 the result of an incipient, acquired habit of but a few weeks' 

 duration, and not really natural to the species or to many of its 

 congeners. Moreover, most of the stealthy stalking movements 

 ended in failure. The actual captures resulted far more fre- 



261 



