no 



ELEMENTS OF BIOLOGY 



ANNELIDA 



COELO» 

 BODY WALL DIGESTIVE CANAL 



EXCRETORY ORGAN 



MOUTH 



NERVE 



FIG. 49. SCHEME OF ANNELID 

 STRUCTURE 



FIG. 50. LEECH 



MOLLUSCA 



FIG. 48 EARTHWORM 



COELOM 



CIRCULA TORY 

 SYSTEM 



MANTLE 



MANTLE 

 CAVITY 



DIGESTIVE 

 CANAL 



SHELL 



GILL 



FOOT 



FIG. 51. PELECrPODA- RIGHT' SHELL FIG. 52 SCHEME OF CLAM STRUCTURE 

 OF CLAM (CROSS SECT/ON) 



Figs. 48, 49, and 50. — Annelida. Fig. 49 is a diagram of general annelid body 



structure, particularly of the anterior region. 

 Figs. 51 and 52. — Mollusca. The right shell of a clam and a diagram illustrating 

 the arrangement of the internal structures of members of the class Pelecypoda 

 when examined in cross section. (Figs. 49 and 52 after Kiihn: Grundriss der allge- 

 nieinen Zoologie. Georg Theime, Leipzig.) 



