ANIMALS WITH JOINTED FEET-THE ARTHROPODS 



211 



skle viev) voitti ri 

 diqcsfive qlanc) 



unnary bladder 

 excretory orqan 

 brain 



opbibaliDic arVcry 



r7X)utb_, 



stDnoGcb 



-ven+ral tboracic arfery 

 -diqcs+ive qland 



ncnxz cord 



an+enocry ar+ery 

 bGDafic arteries 



pericardial ca\)ity 



ovidud-opeoiDq-andvwIkirx] Icq 



sternal arlcry 



sepjinal reccpfocle 



s|3erm duct immature 



sperm duct opemn(]-5ifowolkinq I 

 ovary 



ventrql abdominal arhzry 



dorsal abdominal arfery. 



intestine. 



anus. 



.side view with 

 diqestive qland imact 



Fig. n-n. Internal anatomy of the lobster, both male and female. 



abdominal region. The muscles are at- 

 tached to the internal side of the exoskele- 

 ton, where they are always in pairs, and 

 oppose one another in action. One muscle 

 pulls an appendage or any other part of 

 the body in one direction, whereas the 

 other pulls it back again. The principle is 



followed by all higher animals with skele- 

 tons, including man. 



Digestive system. The chelipeds catch 

 and crush the food, then pass it to the 

 mouth with the aid of the maxillae and 

 maxillipeds (Fig. 11-8). The mandibles 

 break the food up still further, before it is 



