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ESSENTIALS OF ZOOLOGY 



it serves as a support for the heart. The intestine opens 

 posteriorly behind the posterior adductor. The ascending 

 loop in the visceral mass and the remaining posterior part of 

 the intestine is provided with a ridge, the typhlosole, on its 

 ventral surface, and the straight part of the intestine is called 

 the rectum. The whole canal is richly ciliated. 



Aur. 



Ant. ret. 



Ant. 



Post. add. 



Anus 

 Vent. Post. ret. \ Vis.g. \ 



Mouth I Ped.g. Gonad 

 Foot 



Inner gill 



FIG. 30. Anodonta. General dissection from the left side. The nerve 

 commissures are indicated by dotted lines, e.g. = cerebral ganglion. 

 Vis. g. = visceral ganglion. Ped. g. = pedal ganglion, c 1 = outer and 

 c 2 = inner opening of coelomiduct (Coel. d.). Per. gld. = pericardial 

 gland. 



The intestine may be found to contain a peculiar glassy 

 rod, the crystalline style. In the clam, and commonly in 

 Pelecypoda, it occupies a special caecal diverticulum of the 

 stomach. It is produced as a mucous secretion, and becomes 

 rod-like by the action of the cilia. It is believed by some to 

 be a reserve of food for winter, by others to act as an aid to 

 digestion by providing a reserve of enzymes, and it may have 

 a use in preventing rough particles of food from damaging 

 the tender epithelial wall of the intestine. The rod contains 

 proteid material and enzymes. 1 



1 1918. Nelson, Jour, of Morph. vol. 31. 



