2! 12 ELEMENTARY BIOLOGY. [CHAP. 



the lateral tooth. Examine it under a powerful 

 hand lens ; it is beset by short stiff sets. 



5. Carefully remove the alimentary canal, cutting the 

 gullet through close to the stomach; slit open longi- 

 tudinally from beneath, and examine the interior under 

 water. 



a. The crushing surfaces of the lateral teeth ; note that 

 they approximate anteriorly, being obliquely set. 



b. Seize the opposite ends of the stomach between two 

 pairs of forceps and pull them apart. Note that 

 with the divarication of the cardiac and pyloric 

 ossicles the median tooth is elevated (depressed in 

 life) to meet the lateral ones, which are at the 

 same time rotated inwardly and slightly backwardly. 



c. Examine the free border of the chitinous lining; 

 the pyloric valves (4. c. ft) can be well seen from 

 this aspect. 



6. Isolate the stomach of a fresh specimen, together with 

 the adjacent mouth organs. Dissect from the front and 

 remove the anterior half, cutting through the gullet 

 below and the cardiac ossicle above. Wash out the 

 food contents and examine under water. Note — 



a. The median and lateral cardio-pyloric valves 

 (§ 4. b and g) ; they form an efficient straining ap- 

 paratus. 



b. The gastric teeth. Note that they meet, when in 

 action, wholly in front of a. 



c. The lesser cardio-pyloric valves ; three small setose 

 eminences, on either side, adjacent to the lateral 

 teeth. 



