44 THE LEECH. 



two ventro-lateral : each cushion is covered by a thin 

 chitinous cuticle, which is thickened along the free 

 edge of the jaw, and notched into the sharp teeth 

 by which the bite of the leech is produced. The 

 mouth leads, by a very small aperture, into the 

 pharynx. 



Snip away the margin of the anterior stooker-'so as to 

 expose the jaws. Examine them from the ventral surface 

 with a poclcet lens : remove one of them and examine it with 

 a low power of the microscope to see the teeth. 



2. The pharynx is an oval sac with very muscular walls. 



It is connected with the body-wall by strong radial 

 muscles, which give'it a villous appearance, and by 

 their contraction dilate its cavity and produce a 

 sucking action. 



3. The salivary glands are very large granular pyriform 



cells surrounding the pharynx. Each cell is a 

 gland in itself, and is produced into a long stalk or 

 ductile opening on one of the jaws. The secretion 

 has the power of preventing coagulation of the 

 blood, and so very greatly faciUtates the act of 

 sucking. 



Bemove part of the wall of the pharynx, and tease it on a 

 sUde in salt solution. The large pyriform gland-cells, ivith 

 their long ductules, will easily he seen with a low power. 



4. The oesophagus is a short narrow tube leading from the 



pharynx to the crop. 



5. The crop is by far the largest part of the alimentary 



tract. It is a straight thin-walled tube lying in the 

 somites from the fourth to the fourteenth, and giving 

 off eleven pairs of lateral diverticula corresponding 

 to these somites. 



Of these diverticula the anterior two or three 

 pairs are small ; the remainder increase gradually in 

 size from before backwards ; and the hindmost pair 

 are much larger than any of the others, extending 



