14 EARTHWORMS AND LEECHES [CH. I 



segment exhibited a very marked appreciation of the 

 light, being far superior to the other anterior segments 

 in this respect. If the spot of light was thrown a few 

 inches ahead of the moving worm, a sudden start took place 

 directly the prostomium entered the small illuminated 

 area, and the animal withdrew or turned aside: whereas 

 if the light was directed on to any of the first dozen 

 segments, the worm merely paused. Hesse 1 , however, finds 

 that the entire surface is sensitive to light, perception 

 being especially acute at the two extremities. Langdon 2 

 has described sense-cells as occurring freely all over the 

 skin, in great numbers at the front and hind ends, but 

 it by no means follows that these are sensitive to light, 

 they may be merely tactile in function. The sense of 

 smell is undoubtedly possessed by worms, for they will 

 find scraps of favourite food when hidden out of sight, 

 and assemble in quantities in the soil beneath lumps 

 of fat thrown out on the ground. They may often be 

 observed to raise the front end of the body and wave it 

 in this or that direction in the air, as though they were 

 obtaining information that reached them through the air, 

 i.e. as odours. 



The prostomial lobe, or upper lip, seems to act as 

 a special tactile, or perhaps also taste organ, and may often 

 be seen thrust forward in a tentative manner and speedily 

 withdrawn by telescoping into the segments behind if the 

 object explored be distasteful. No doubt the whole surface 

 of the body is highly sensitive to touch, and to certain 



1 Zeit. wiss. Zool LXI. 1895-6. 2 j ourn . Morph. xi. 1895. 



