192 



ZOOLOGY. 



body immediately surround the mouth, and are so constructed 

 as to form instruments of locomotion, instruments of pre- 

 hension by their free extremities, and of jaws by their base ; 

 but, as might be anticipated, this very cumulation of func- 

 tions renders them less appropriate for the advantageous 

 performance of any special function. But in animals of the 

 same class with faculties more perfect, these different func- 





'1 'V 



Fig. 142. Limulus.* (Molucca Grab.) 



tions are no longer performed by one and the same organ or 

 instrument ; each function belongs to a distinct organ, and 

 yet these organs are still the same limbs or members, of 

 which some are exclusively destined to mastication, others to 

 prehension, and others to locomotion. In the craw-fish (ecre- 

 visse), or lobster, for example (Fig. 143), the limbs sur- 

 rounding the mouth are exclusively arranged for mastication; 



* The animal is represented as seen from below : J, the mouth ; />, feet 

 whose base performs the office of jaws j a, abdominal appendages carrying 

 branches ; q y caudal stylet. 



