ARTICULATED ANIMALS. 



81 



and it is in the abdomen only that the segments of 

 the body are recognizable. By contrasting the body 

 of a centipede with that of a scorpion, as represented 

 in the accompanying figure (Fig. 55), the progress 

 of this coalescence of the tegumentary rings is 

 strikingly exemplified. 



Lastly, in the Crustacea (crabs, lobsters, $c.) we 

 find various modifications of the outward skeleton 

 adapted to the habits of the different races. Among 

 the lowest forms, the rings composing the external 

 framework are perfectly distinct and separate, resem- 

 bling those of the myriapoda ; but in the stronger and 

 more predacious tribes the pieces of the head and 

 thorax become solidly fixed together ; and in those 

 forms most adapted to a terrestrial life, namely, the 

 crabs, almost all traces of distinction between the 



FlG. 56. COMMON CRAB. 



thoracic segments is lost in the construction of the 

 calcareous shield, which covers and protects their 

 whole body. (Fig. 56.) 



In the animals described in preceding chapters the 



E 3 



