54 THE LEECH. 



two ventrolateral : 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 sucker so as to expose 

 the jaws. Examine them from the ventral surface with a pocket 

 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 facilitates the act of 



sucking. 



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



slide in salt-solution. The large pyriform gland-cells, with 



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



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



pharynx to the crop. 



5. The crop consists of eleven chambers, separated by 



partitions, each perforated by a circular or trans- 

 versely oval opening, surrounded by a sphincter 

 muscle. The partitions may be demonstrated by 

 cutting transversely across the dorsal face of one 

 of the larger posterior chambers, and pulling the 

 lips of the cut away, so that the partitions lie 

 nearly horizontal, and their perforations are clearly 

 seen. From each chamber a pair of lateral sacs, 



