ANATOMY OF THE EARTHWORM. 143 



the posterior segments, a milky fluid, the perivisceral 

 fluid. Place a drop of the fluid on a glass slide, 

 gently cover it, and examine it under a microscope. 

 It consists of a coagulable, albuminous plasma, which 

 contains great numbers of transparent, granular, amoeboid 

 corpuscles. In addition to these normal constituents, it 

 usually contains foreign bodies, such as Gregarinee, para- 

 sitic Infusoria, and Xematoid worms, broken setae, etc. 



2. The muscular dissepiments, or diaphragms, which 

 extend inwards from the integument to the wall of the 

 digestive tract, and imperfectly separate the body cavities 

 of adjacent segments. 



3. The digestive tract, a nearly straight tube, without 

 convolutions, extending along the median line of the body 

 from the anterior to the posterior end. 



4. Upon its dorsal surface, and closely united to its 

 wall, observe the red dorsal or supra-intestinal blood- 

 vessel. 



5. The digestive tract is divided into several well- 

 marked regions : 



a. The pharynx, a large, broad, muscular organ (Fig. 

 84, ?i), extending from the second to the seventh seg- 

 ment, and similar, in shape and connections, to the suck- 

 ing chamber of the leech. 



(i.) The radiating muscular fibres which bind it to the 

 integument. 



(ii.) The cephalic or supra-cesophageal ganglia; two 

 pear-shaped bodies (Fig. 84, a), upon the dorsal surface 

 of the pharynx, in the third segment of the body, and 

 united to each other by their broad ends upon the dorsal 

 median line. 



From their smaller outer ends arise two fibres, which 

 pass down around the pharynx to unite with the ventral 

 nerve chain. 



