40 CRUSTACEA 



(3) Plan of circulation of blood of the era} fish. From heart 



to From to From 



to the heart. 



(a) Any veins? Any capillaries?^ 



(b) How is the circulation kept up? 



(c) Why is the circulation kept up? 



2. The Respiratory System. 



(1) The Gills. With sharp scissors cut away the cara- 



pace from one side of the cephalothorax, exposing 

 the white, feathery gills. Dissect under water. 



(a) Number of gills attached to the base of each leg? 



Remove each leg with your forceps and see. 



(b) Number attached to body wall? 



(c) Total number on one side? 



(d) Total number on both sides? 



(e) What does Huxley's ''Crayfish" say as to the number 



of gills in the Enghsh crayfish (genus Astacus)? 



(f) Does our crayfish (Cambarus) have the same number 



of gills as the Enghsh crayfish? 



(g) Use of the gills? 



(h) Do you see that they are really on the outside of the 

 body wall, i. e., are external organs? 



(2) Plan of the respiratory system. 



(a) How connected with the circulatory system? 



(b) Why connected with the circulatory system? 



3. The Digestive System. 



(1) Mouth-parts. (Mandibles, etc.) 



(a) Name parts concerned in prehension. 



(2) The Mouth. Find it with your probe. 



(a) Shape? 



(b) Size? 



(c) Location? 



(3) The Gullet. Find this short tube leading into the 



wide stomach. Use? 



(4) The Stomach. With scalpel very carefully cut away 



the top of the head and expose the large, thin-walled 

 stomach. 

 (a) Color? 



iSee Huxley's "Crayfish," pp. 69-74. 



