312 Biology in America 



this turning may bring it towards, rather than away from 

 tlie unfavorable medium. Its behavior in this case is fixed in 

 character, and not so clearly mechanical as in the former 

 case. 



A remarkable imitation of a living creature responsive to 

 light stimuli has been invented by the American engineer 

 John Hays Hammond, Jr. It "consists of a rectangular box 

 about 3 feet long, li/o feet wide and 1 foot high mounted on 

 three wheels, two of which are geared to a driving motor, 

 while the third and rear wheel can be turned by electro- 

 magnets and thus serve for guiding the machine. Two 5-inch 

 condensing lenses on the forward end appear very much like 

 large eyes. ' ' The operation of the machine is affected through 

 the action of light on two selenium cells controlling electro- 

 magnetic switches. "When one cell or both are illuminated 

 the current is switched on to the driving motor ; when one cell 

 alone is illuminated an electro-magnet is energized and aifects 

 the turning of the rear steering wheel . . . thus bringing the 

 shaded cell into the light. As soon and as long as both cells 

 are equally illuminated in sufficient intensity, the machine 

 moves in a straiglit line toward the light source. By throw- 

 ing a switch which reverses the driving motors, the machine 

 can be made to back away from the light in a most surpris- 

 ing manner. 



"Upon shading or switching off the light the 'dog' can be 

 stopped immediately, but it will resume its course behind the 

 moving light so long as the light reaches the condensing 

 lenses in sufficient intensity. Indeed, it is more faithful in 

 this respect than the proverbial ass behind the bucket of 

 oats. To the uninitiated the performance of the pseudo dog 

 is very uncainiy indeed."* 



But what is the case with those animals with a nervous sys- 

 tem by means of which their complex functions are made to 

 work in orderly fashion? It would take us too far afi<'ld to 

 attempt to trace, as Professor Parker has recently done in his 

 admirable little book on the "Elementary Nervous System," 

 the relation between the specialization of the latter, and the 

 (delicacy) of their nervous responses. Suffice it to say that 

 even in animals with a highly developed nervous system such 

 as insects the responses in many cases at least appear to be 

 purely mechanical. The attraction of the candle flame for 

 the moth is proverbial, and even so highly organized an animal 

 as a bird fre(|uently appears to be as much a creature of cir- 

 cumstance as the moth, for birds often beat themselves to 

 death in great numbers against light-houses. The purely 

 mechanical response of an animal to stimuli is beautifully 



^Mit'ssner, "Electrical Experimenter," Sept., 1915, p. 202. 



