52 



MOLLUSC A. 



throat, as a muscular bulb, with its continuation in the 

 flattened, thin-walled tube of the alimentary canal, is also 

 better seen from the upper side. The generative organs 

 are thrown out of place in Fig. 25. They really cover the 

 intestine, and crop from view, and have to be treated in 

 this way to give a view of these parts. 



Slit open another specimen on the upper side, beginning 

 between the tentacles. 



Lying above the other organs are the two inverted tubes 

 of the upper pair of tentacles, distinguished by their dark- 

 colored interiors ; and below them, but partially hidden, 

 those of the lower pair ; both of these are exserted in the 

 figure, however. Just around the throat the nervous collar 

 and its ganglia show plainly. 



Slit open the throat, or slice a head in two after harden- 

 ing it in alcohol, and notice the two cartilages upon which 

 the tooth or jaw rests, and the slightly-roughened tongue 

 behind, with its horny surface (Fig. 26). 



Introduce a probe into the throat and alimentary canal, 

 and observe how the motion of the tooth in scraping sur- 

 faces would at the same time place food within the reach 

 of the lips, and the tongue, by moving back and forth, would 

 help to comminute the food. Follow the alimentary canal 

 backwards, and notice at the same time the ovaries, and how 

 they run back into the spire, and the other generative 

 organs attached to the sac of the dart on the right side. 

 The alimentary canal will be found to expand into a large 

 so-called crop underneath the pulmonary sac ; and after 

 that it passes directly onward into the spire to st, whercf 

 the true stomach occurs. Then, turning abruptly down, it 

 crosses around to the point /, and making the bend as in 

 the figure, returns around the spire to i; and from thence 

 again circles around to /, and passing along the floor of the 

 pulmonary sac, terminates at the anus {afi), alongside of 

 the pulmonary opening in the thick border of the mantle. 

 Between the bends of the intestine are the brownish 



