LITTIOBIUS 97 



Finally, the blind crayfish deserves a further word besides 

 the brief reference in Chapter VIII. Most boys know that 

 all crayfishes love the darker parts of streams, and when placed 

 in strong light, they act as though it were painful to them. 

 As they live in streams they would, in cavernous countries, 

 often be brought to the point where a stream issues from a 

 cave. The darkness of the cave would be a lure to them. 

 Consequtnitly some of them in time would come to be perma- 

 nent inhabitants of it. The loss of sight and pigment would 

 follow. 



Thus we see, in general, that the fauna of caves is not an 

 accidental one, nor one made up of accidental!}^ associated 

 animals. It is a society of light-shunners. They are lucky 

 to have a cave to live in. 



Lithobius belongs to the group Myriapoda,' which is closely 

 allied to insects, but is characterized by life in dark, moist 

 places. The Myriapoda differ from most insects in being 

 wingless and in having the body divided into two regions, 

 head and trunk, and in having either one or two pairs of legs 

 on each segment of the trunk, so that there are, all together, 

 many pairs of legs instead of only three as in insects. 



There are two principal groups of M3Tiapoda, the Centipedes 

 and the Millipedes. The Centipedes (Chilop'oda ^), to which 

 group Lithobius belongs, have only one pair of appendages 

 to each body segment. They are active and ferocious animals. 

 All are terrestrial and live chiefly under stones and bark, within 

 or under decaying wood, among barn-yard refuse, in loose 

 soil, and under fallen leaves. Chilopods feed upon U^dng 



^ myrios, very many; pons, foot. 



2 More correctly C'heilopoda, from cheilos, lip, and pous, foot; because 

 the mouth parts (modified feet) are partially united to form a sort of lip. 



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