GENERAL BIOLOGY 



3. A mesh work of fine fibres. 



4. Very large clear "giant fibres" each in a definite sheath. 



5. In some of the sections the nerves are to be seen as they pass 

 from ganglion cells to the body wall. 



IV. BODY CAVITY. 



Some of the sections will show the following structures : 



1. The corpuscles of the coelomic fluid. 



2. Blood vessels cut across and filled with coagulated blood. 

 2. Mesenteries or dorsal and ventral membranes connecting the 



digestive tract with the body wall on the median line. 



4. Septa and nephridia cut at various angles. 



Make a full-page outline of a cross section to show all of these 

 organs and in the ventral sector fill in histological details of (a) 

 Body Wall, (b) Body Cavity and Nervous System, (c) Digestive 

 Tract. 



CAMBARUS, The Crayfish. 



(Phylum Arthropoda, Class Crustacea.) 



Read: Huxley, The Crayfish, pp. 1-226; also 



Parker and Parker, Practical Zoology, pp. 346-37-; or 

 Calkins Biology, pp. 166-186. 



A. GENERAL CHARACTERS. 



I. BODY. 



Note that the animal has a body proper and a series of paired 

 appendages. The body is bilaterally symmetrical and divided into 

 a posterior jointed abdomen and an anterior portion the cephalo- 

 thorax. The entire body is covered by a hard calcarious shell the 

 exoskeleton which is flexible at the joints where movement may 

 take place. 



II. APPENDAGES. 



Note that all of the appendages are jointed that they are attached 

 in pairs to the ventral surface of the body and that they vary much 

 in sz'ze and form. 



Make a drawing of the crayfish as seen from the dorsal side. 



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