EARTHWORMS 167 



across the otherwise green surface. Fat and animal grease of 

 every kind is a very favourite article of diet. If some such sub- 

 stance is buried in the ground the worms throng towards it. It 

 is thus evident that they have a sense of smell, though no definite 

 organ for the purpose has been identified. The sense of taste, 

 which is closely allied to that of smell, is possessed by the upper 

 lip, which is a small projection beyond the first segment and 

 above the mouth. It is thus probable that powers of smelling 

 reside here also. Incidentally it may be mentioned that the shape 

 of the upper lip is not the same in all earthworms, and the 

 variations in its form constitute one of the features by which the 

 different species are recognised. 



With other, special senses the worm is not liberally endowed. 

 It is absolutely deaf, but on the other hand is so extremely sensi- 

 tive to vibrations of the soil that the would-be observer must 

 approach most cautiously to avoid causing alarm. No doubt 

 this acute perception is of value in giving warnings of the approach 

 of the mole. Again, there are no eyes, but the skin as a whole, 

 and especially in the front region of the body, can distinguish 

 between light and darkness. This sensibility can be demon- 

 strated by suddenly flashing a bright light, with the aid of a 

 mirror, on to an undisturbed worm : the moment the light reaches 

 the body the animal recoils. 



Weather. During periods of drought or of frost worms retreat 

 from the surface into the deeper parts of the soil, often descending 

 several feet in order to escape adverse weather. Here the animal 

 empties its body of soil, and excavates a small chamber, in which 

 it coils itself up into a close spiral and remains dormant until 

 more favourable conditions set in. The walls of the chamber 

 are often lined with small pebbles, the air between which is doubt- 

 less of value as a non-conductor of heat. It is often noticeable 

 that after very heavy rains many worms are found crawling 

 aimlessly Upon the surface, and frequently in a moribund con- 

 dition. It is not clear why they behave in this way : no doubt 

 the moisture-sodden ground causes them some discomfort, poss- 

 ibly it may render breathing difficult by expelling the air from 

 the interstices of the soil ; but since worms can survive immersion 

 in water for several hours this factor cannot be of great importance. 



