72 



ANATOMY OF CRUSTACEANS. 



a a 



an 



qbr p p p br 



Fig. 62. ANATOMY OF CRUSTACEANS LOBSTER. 



commonly supported by solid plates, and internally furnished 

 with very hard teeth. The intestine is narrow, and on each side 

 <}f this tube we see the liver (/), which is generally very volu- 

 minous ; but sometimes we find simple biliary vessels substituted 

 for it. 



8. The heart of crusta'ceans (c) is situated near the back, about 

 the middle of the thorax ; it is generally of considerable size, 

 and consists of one ventricle only, which forces the blood through 

 the arteries. After having furnished nutritious material to the 

 various organs, this liquid goes to the venous sinus placed "along 

 the base of the legs, thence to the respiratory organs (br), and 

 then returns to the heart. The heart of crusta'ceans is aortic, 

 and the circulation is carried on nearly in the same manner as in 

 mollusks. 



9. The respiration of crusta'ceans is almost always aquatic, 

 and is effected by means of branchiae (br). These organs vary 

 both in form and situation; but they are generally attached near 

 the base of the legs. 



10. All crusta'ceans are ovi'parous; after laying her eggs, the 



Explanation of Fig. 62. Anatomy of Crusta'ceans. A lobster seen in 

 profile, the greater part of the integuments being removed ; c, the heart; 

 a, o, the abdominal artery ; as, the sternal artery ; a, artery of the 

 antennse ; e, the stomach ; m, muscles of the stomach ; /, the liver; 

 br, branchiae ; p, buse or point of insertion of the legs ; ca, part .of the 

 carapace ; b, the mouth ; r, the respiratory canal destined to give passage 

 to water for the purpose of respiration ; y, the eyes ; an, the superior 

 antennae; ant, base of the inferior or second pair of antennae ; q, the 

 caudal fin, the principal organ of progression. 



8. What is the character of the circulation ? 



9. How do crusta'ceans breathe ? 



10. How are the young of crusta'ceans produced ? 



