ADAPTATION 



221 



to the lower limb of a vertebrate, and these guarantee a non-sldd 

 take-off from any surface providing the slightest of holds. For 

 obvious reasons only the hind legs of jumping insects are special- 

 ized. 



Fossorial Adaptations. In contrast to cursorial and saltatory 

 adaptations, fossorial species have the front legs most highly 

 developed, since they must open a way for the body through the 

 earth. Among the invertebrates without appendages burrowing 

 is accomplished by the simple means of forcing the slender, tapering 

 body through relatively loose soil, or by passing earth through 

 the alimentary tract as the animal progresses. Arthropoda, how- 

 ever, make use of the mouth parts and of the legs in digging. An 

 extreme specialization of this type is seen in the mole-cricket, 



Fig. 130. — Common mole, Talpn europnea, showing skeleton and outline of 

 body. (From Lull, after Pander and D'Alton.) 



whose front legs are strong, notched, shovel-like appendages with 

 which the insect digs rapidly and effectively (Fig. 128C). These 

 strange httle creatures are also covered with moisture-resisting 

 down. 



The mole is the most highly specialized fossorial vertebrate 

 since it lives entirely undergrovmd (Fig. 130). Its pectoral girdle 

 and fore-limbs are massive, and the forefeet are very broad and 

 provided with strong claws. In addition to this elaborate mech- 

 anism it has an elongate pointed snout which aids it in forcing its 

 way rapidly through soft earth. Its progress may be a combina- 

 tion of digging and spreading of the earth before it. The mole, 

 like its namesake, the mole-cricket, has extremely fine vestiture, 

 resistant to moisture. The eyes are vestigial in the mole, and the 

 external ears are lacking. Either organ would be liable to injury 

 in burrowing, and neither could be of use to an animal whose hfe 

 is spent in darkness surrounded by solid earth. 



Many other vertebrates representing all classes above the fishes 

 are fossorial, though they do not remain altogether underground. 



