122 ZOOLOGY 



in shallow water, or it can swim free in the water. By suddenly 

 striking the tail fin forward the lobster can dart backward, 

 trailing the great claws in the wake. The strokes of the power- 

 ful tail also tends to roil the mud of the bottom and thus to 

 hide the retreat of the animal. Although the body is encased 

 in a cuticula of great thickness and firmness, yet the presence 

 of thin-skinned joints makes not only the abdomen but also 

 the largest of the appendages capable of complex movements. 



Organs and Functions of Nutrition. — The lobster feeds 

 principaUy upon fish, either dead or alive, upon various other 

 Crustacea and mollusks, and also upon marine plants. The 

 food, held in place by the mouth-parts, is triturated by the 

 jaws and passes bj' a short gullet into the stomach.' The 

 outer cuticula is turned in at the mouth and hnes not only the 

 gullet but also the stomach. In the :;tomach it is thickened 

 and hardened in three points to form " teeth " which, in the 

 muscular movements of the stomach, clash together in such 

 a wa\' as to crush any larger particles that have escaped the 

 mincing of the jaws. Digestion takes place in the succeeding 

 part of the food canal which runs nearh' straight to the last 

 segment of the l)ody. A great gland (liver) secretes the diges- 

 ti-\'e juices and empties them at the beginning of the intestine. 

 Beyond the opening of the gland the absorption of the digested 

 food takes place through the wall of the canal. 



Organs and Functions of Respiration. — Oaring to the fact 

 that the loljster lives in the water from which it takes its 

 oxygen, the respiratory organs are outgrowths of the body 

 instead of internal tubes as in insects. Such outgro-wths are 

 called gills. Gills must have thin walls to allow of the passage 

 of gases through them ; tliey must lie much branched to make 



iFig. 123. 



