Morse, Reactions of the Larva of Tenebrio Molitor. 723 



Immediately beneath the chitin is a single layer of deep cells with 

 conspicuous nuclei, and these cells pass into a region of yet deeper 

 (longer) cells as we pass from the pigmented area. There is thus left, 

 in the region of the pigment, a space containing the pigment and a 

 granular material of apparently homogeneous constitution. The pig- 

 ment is grouped in two cups into the bases of which delicate fibers, 

 presumably nerve fibers, enter. I have not been able to determine 

 from my material, whether there are any elements which might be 

 light-receiving in function within these cups, i. e., between the pig- 

 ment and the layer of cells lying immediately beneath the chitin. The 

 pigment seems to be absent from the region at the bases of the cups, 

 where the fibers enter, and the sensory organs may lie in this region. 

 The fibers lead from the pigment bodies posteriorly, where the two 

 sets join and then, turning laterally, pass out into the cellular mass 

 at the sides and in the rear of the eye-spots, where they become indis- 

 tinguishable. I have not been able to examine the eyes in a neuro- 

 logical stain, as should be done, but the general character of these 

 organs may be gained from this brief study. 



Observations. 



The body surface as a whole is sensitive to light of great intensity. 

 A larva was placed in a rubber tube 5 cm. long, having a bore such 

 that the worm fitted snugly within it. The anterior end of the larva 

 was directed towards the sunlight which fell obliquely upon the tube. 

 The larva soon began to crawl backward and finally the tip of the 

 abdomen was pushed out of the tube into the sunlight for three or 

 four segments. Immediately the worm reversed its direction of 

 motion and crept back into the tube. A heat-filter had been interposed 

 between the sun and the tube and cooled paper had been introduced 

 beneath the tube, so that heat reactions were eliminated. The same 

 reaction was observed in cases where the tip of the abdomen became 

 exposed to the sunlight as the worm maneuvered in the shadow and 

 inadvertently threw its abdomen outside the shadow. When the tip 

 of the abdomen, which had previously been painted with a mixture 

 of lampblack and vaselene, was exposed to the sunlight, no reaction 

 followed. 



