GENERAL BIOLOGY 



c. Fine vessels seen upon the septa, body walls and the 

 nephridia. 



III. COELOMIC FLUID. 



Puncture the body where not yet opened and take out in a fine 

 pipette some of the fluid of the body cavity, examine under a high 

 power and note : 



1. White amoeboid corpuscles. 



2. Yellow granules, from the chlorogogue cells (See D II. i). 



3. Bacteria or other foreign bodies, especially Gregarina, which 

 are often present. 



D. HISTOLOGY. 



I. BODY WALL. 



Examine prepared transverse sections of the body ; observe body 

 wall, now seen to be made up of five layers : 



1. Cuticle, a thin non-cellular layer (membrane) often torn off. 



2. Deric epithelium or epidermis, a single layer of cells many 

 of which are swollen (gland .cells). 



3. A thin outer layer of circular muscle fibres with blood ves- 

 sels and connective tissue nuclei among them. 



4. A thick layer of longitudinal muscle fibres or plates, ar- 

 ranged in elongated groups of elliptical form. 



5. Peritoneum or coelomic epithelium, a thin layer of granular 

 protoplasm containing nuclei, lining the body cavity. 



II. DIGESTIVE TRACT. 



In its wall four layers are to be seen. 



1. Chlorogogue cells, large and more or less elongated and 

 irregular. 



2. An outer layer of longitudinal muscle fibres cut across. 



3. A layer of circular muscle fibres and of blood vessels (not 

 easily made out). 



4. Enteric epithelium; a single layer of elongated cells with 

 stained nuclei and a thin cuticle over their central ends through 

 which fine cilia project into the lumen of the gut. 



III. NERVOUS SYSTEM. 



In a transverse section of the ventral cord, note : 



1. An outer muscular sheath or coat. 



2. Large ganglion cells in groups or clusters. 



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