38 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



" brain " ; note the tendency of ganglia to fuse into larger 

 nerve centers (Figs. 55, 267). 



Exhibit a series of larval crayfishes or lobsters, show- 

 ing the changes undergone at each molting. 



Try to get specimens of the lobster, showing the re- 

 generation of lost parts, specially the pincers. 



Call attention to resemblances in structure between 

 earthworm and crayfish ; note in the latter the tendency 

 to collect into definite regions the organs devoted to 

 definite uses ; also that every segment bears a pair of 

 jointed appendages. 



Use the crab (Callinectes} for comparison. 



2. INSECTA 

 Grasshopper 



Living specimens may be kept in boxes or jars cov- 

 ered with gauze or netting and kept supplied with plenty 

 of fresh grass or wheat. 



Field and Vivarium Study, Note how the insect 

 walks, leaps, and flies ; the length of a single leap ; how 

 the food is held and eaten ; the use of the various sense 

 organs, as eyes and feelers; the mode of breathing; 

 the protective coloration of the body. 



Structure. Note the three regions of the body (head, 

 thorax, and abdomen), comparing with crayfish and 

 spider ; study the structure of each region ; the appen- 

 dages borne by each region ; their use ; the structure of 

 each kind of appendage and its adaptation to t its special 

 function ; the spiracles ; the ovipositor on the female ; 

 the ear (Figs. 64, 219, 276, 295, 344, 352). 



Cut open a specimen lengthwise and note the parts 

 of the digestive system ; the muscles ; the reproductive 

 organs ; the structure and arrangement of the nervous 

 system. Examine tracheal tubes with the microscope 

 (Figs. 239, 277, 278). 



