The Living Machine 319 



those which they produce in nerves, we have good reason to 

 believe that their action on the latter is similar to that on 

 the former or that the prevention of nervous action, and 

 therefore that action itself is fundamentally a physico-chem- 

 ical one. 



But can physics and chemistry explain all the complicated 

 instincts of the insect, bird and mammal, or the as yet un- 

 solved riddle of human thought? Frankly we must admit 

 that at present we do not know. According to Loeb these 

 are merely ''tropistic reactions" modified by "memory 

 images," which have an "orienting effect" upon the organ- 

 ism, and which he attempts to explain by an illustration 

 from the behavior of the solitary wasp Ammophila, which 

 digs a hole in the ground in which to lay its eggs. 



Ammophila, a solitary wasp, makes a small hole in the 

 ground and then goes out to hunt for a caterpillar, which, 

 when found, it paralyzes by one or several stings. The wasp 

 carries the caterpillar back to the nest, puts it into the hole, 

 and covers the latter with sand. Before this is done, it de- 

 posits its eggs on the caterpillar which serves the young larva 

 as food. 



"An Ammophila had made a hole in a flower bed and left" 

 the flower bed flying. A little later I saw an Ammophila 

 running on the sidewalk of the street in front of the garden, 

 dragging a caterpillar which it held in its mouth. The 

 weight of the caterpillar prevented the wasp from flying. 

 The garden was higher than the sidewalk and separated from 

 it by a stone wall. The wasp repeatedly made an attempt 

 to climb upon the stone wall, but kept falling down. Sus- 

 pecting that it might have a hole prepared in the garden, 

 I was curious to see whether and how it would find the hole. 

 It followed the wall until it reached the neighboring yard, 

 which had no wall. It now left the street and crawled into 

 this yard, dragging the caterpillar along. Then crawling 

 through the fence which separated the two yards, it dropped 

 the caterpillar near the foot of a tree, and flew away. After 

 a short zigzag flight it alighted on a flower bed in which I 

 noticed two small holes. It soon left the bed and flew back to 

 the tree, not in a straight line but in three stages, stopping 

 twice on its way. At the third stop it landed at the place 

 where the caterpillar lay. The catei-pillar was then dragged 

 to the hole, pulled into it, and the hole was covered with tiny 

 stones in the usual Avay. ' ' ^° 



Aside from the fact that we have no explanation of the 

 physico-chemical processes underlying these "memory 

 images," it is difficult to apply the theory to many of the 

 "Loeb, locus citatus, p. 170. 



