TERRESTRIAL 



;entacles, and the eyes on the tips of the longest pair, and the 

 large breathing opening on the right-hand side which leads into 

 a " pulmonary chamber/' formed by a dorsal fold of skin (the 

 mantle), and bearing a network of blood-vessels on the internal 

 surface of its roof. Some should be made to creep on a plate of 

 glass so as to show the beautiful waves of muscular contraction 

 passing along the so-called " foot/' which is simply a flat muscular 

 development of the ventral surface. It is profitable to collect 

 some specimens for the vivarium, so that their characteristics 

 may be studied at leisure, e.g. their omnivorous appetite, their 

 keen sense of smell, their fondness for bathing. The pupils may 

 perhaps discover the slugs laying eggs, and find out something 

 new. From another point of view it is interesting to notice that 

 while the common snails (Helix) have well developed shells, and 

 most slugs (like Limax) have flat vestiges hidden on their back, 

 the species of Arion have lost the shells entirely, or have only a few 

 calcareous granules on their back. From another point of view 

 it is worth noticing that the black slug is a good example of the 

 distinctively northern contingent of British animals. 



Ant-Hills. Among the sights of the woods are the ant-hills, 

 which should be carefully studied In many of the pine-woods 

 they attain huge dimensions, four feet high and ten feet in cir- 

 cumference, and are chiefly built of the needle-like leaves and 

 small twigs of the Scotch fir. There are many things to be done, 

 to look for some of the main paths leading into the hill, to see 

 what the workers are carrying in, to give them various kinds of 

 things to carry, e.g. cow-wheat seeds which are very like ant 

 pupae, to put obstacles in their way and observe how they meet 

 them, to disturb a small part of the hill to see the workers carrying 

 the pupae in their mouths. The white pupae, sometimes called 

 ants' eggs, sometimes called cocoons, should be explained ; they 

 are the stages between grubs and adults, and correspond to 

 chrysalids. The grub is undergoing metamorphosis within the 

 pupa-case. It should be pointed out that cocoon meant some- 

 thing quite different in the case of the spiders on the moor. 

 Care must be taken to leave the general impression clear that 

 the ant-hill is a more or less permanent city, though it may be 

 shifted from one place to another ; that it may be older than its 



