262 



CRUSTACEA. 



teeth, and gastroliths in the " stomach," is intelhgible when 

 the origin of the fore gut is remembered, and so is the dis- 

 mantled state of this region when moulting occurs. 



The mid gut is very short, but it is the digestive and 

 absorptive region. From it, there grows out on each side a 

 large digestive gland with two ducts. This gland is more 

 than a "liver," more even than a " hepatopancreas." It 

 absorbs peptones and sugar, and makes glycogen like the 

 Vertebrate liver, its digestive juices are comparable to those 

 of the pancreas and the stomach of higher animals. The 

 hind gut is long and straight. It is lined by a chitinous 



H G 



Fig. 84. — Longitudinal Section of Lobster, showing some 

 of the organs. 



//, Heart ; A.O^ ophthalmic artery' ; a. a, antennarj' arterj' ; a.h, 

 hepatic artery ; St, sternal artery ; S.A, superior abdominal arter>' ; 

 M.G, mid gut : D.G, digestive gland ; H.G, hind gut ; Ex, exten- 

 sor tnuscles of the tail ; Fl, flexor muscles of the tail ; I. A, inferior 

 abdominal artery ; G. gizzard ; C, cerebral ganglia. 



cuticle, as its origin suggests. There are a few minute 

 glands on its walls. 



Bodv Cavitv. 



The space between the gut and the body wall is for the 

 most part filled up by the muscles and the organs, but 

 there are interspaces left which contain a fluid with amceboid 

 cells. These interspaces seem to represent enlarged blood 

 sinuses (a ha;moccele) rather than a true body cavity or 



