Sfi-aditi'e of an Aastrallan Land Leech. 225 



Besides the outer circular and inner longitudinal muscles of the 

 pharynx, there is a series passing in a radial direction from the 

 inside epithelial lining to the circular muscles on the outside. 

 These are the radial muscles (R.) and they occur only in the 

 pharynx. The function of this part of the alimentary canal is to 

 draw by suction action the blood, necessary for food, from animals 

 to which the leech becomes attached. 



The niuscular pharynx (ph.) gives place about the middle of 

 somite VI. to the oesophagus. This is a tube with glandular 

 walls, surrounded by circular muscles. The glands are what I 

 take to be the salivary glands, racemose in appearance, consisting 

 of somewhat large clear cells and opening by very short-necked 

 narrow ducts in the cavity of the oesophagus. This extends 

 through somite VII. where it opens into the crop (Fig. 2), which 

 evidently corresponds to the "stomach" in forms described l)y 

 Oka and Whitman. The crop is a comparatively thin walled 

 tube giving off eleven pairs of diverticula, one pair in each of tlie 

 somites VIII. -XVII., while the eleventh pair opens in somite 

 XVIII. and runs back parallel to the intestine as far as somite 

 XXI. The wall of the alimentary canal in this region consists 

 of circular muscle fibres, and a columnar epithelial lining. The 

 alimentary canal throughout its whole length is well supplied with 

 blood vessels. Opening from the crop is a short tube lead- 

 ing directly into the intestine and occupying somites XIX., 

 XX., and XXI. (Fig. 2). This is the stomach. Its walls differ 

 from those of both crop and intestine, in that they are made up of 

 columnar epithelial cells very closely set and almost double the 

 height of those of the crop. On the outside are muscular fibres — 

 circular and longitudinal, among which lie the capillaries and 

 numerous blood vessels. In this part of the canal digestion goes 

 on chiefly, and from the good supply of blood vessels it would 

 appear that absorption also takes place. 



The intestine passes from the stomach in the 73rd annulus 

 to the extreme posterior end where it opens to the exterior by the 

 anus (Fig. 4, An.), situated on the doi'sal surface in the little 

 groove wiiere the acetabulum joins the body wall. The wall of 

 the intestine resembles in appearance that of the crop — that is 

 short columnar epithelium thrown somewhat into folds so as 

 to increase the surface. It is richly supplied with blood vessels 

 and surrounded by muscular fibres. ioa 



