HELIOTROPISM OF ANIMALS 67 



Decaying meat has the same attractive effect on the larvae of 

 flies. If such animals are in a test-tube containing decaying 

 meat, and the tightly fitting cork is loosened a little, the 

 animals which were crawling between the meat and the open 

 end of the tube turn and go back toward the meat. I mois- 

 tened a small area on a plate by rubbing it with decaying meat. 

 I placed some half -grown larvae which I had taken from the 

 meat in the middle of this moist surface. They at first crept 

 toward the room side of the plate, but turned when they 

 came to the boundary of the surface smeared with the putrid 

 meat, and remained within it. Not until half an hour later, 

 when the spot had dried completely, did they leave it. 

 When I merely moistened a spot on the plate with pure 

 water, the larvae did not remain on it. 



When I removed the animals from a cadaver and placed 

 them on a glass plate, and brought a piece of decaying meat 

 into their neighborhood, the animals crept toward it, even if 

 in so doing they were obliged to move toward the window ; 

 this occurred, however, only when the animals were in the 

 immediate neighborhood of the meat. When they were 

 more than a centimeter and a half away from the meat, they 

 were no longer attracted by it ; they then followed the direc- 

 tion of the rays of light and starved in the neighborhood of 

 food. Animals which had not yet tasted food were also 

 attracted by the decaying meat. Fat, even when foul, 

 attracted the animals only slightly or not at all ; this is very 

 remarkable, as the female flies are also more readily attracted 

 by meat than by fat. I often placed a piece of horse flesh 

 and a piece of horse fat side by side in the sun. At a time 

 when the flesh was covered with eggs, the fat was almost free 

 from them. It seems, therefore, as though the same chemical 

 stimulus which attracts the larvce causes the flies to deposit 

 their eggs. Decaying cheese also attracted the larvae, but 

 ammonia and assafoetida were without effect. Some volatile 



