206 ELEMENTARY BIOLOGY. [CHAP. 



the hinder border of the mandible, to be attached 

 to the cephalic shield, slightly in front of the cervical 

 groove. Note its powerful tendon. 



Small muscles will be seen, passing from the man- 

 dible and antennary organs to the adjacent exo- 

 skeleton. 



e. Lay bare the basal portion of the great chela, and 

 note the relations of its muscles. They arise from 

 the endophragmal system, and are attached to 

 tendinous ingrowths of the appendage itself similarly 

 to those described in 2. 



D. The general disposition of the viscera. 



i. Place the animal on its ventral side and pin down 

 under water, inserting the pins through the tail fin 

 and bases of the chelae; remove the whole tergal 

 skeleton and with it the extensor abdominis muscle. 

 Note in order 



a. The alimentary canal; a straight tube, running the 

 whole length of the body in the middle line. It is 

 greatly enlarged in front to form the so-called 

 stomach, which fills the greater portion of the 

 cephalon. 



b. The heart ; a slightly yellowish pentagonal organ of 

 delicate texture, lying above a in the middle thoracic 

 region. 



c. The genital gland. In the female, a yellowish brown 

 mass ; in the male, a whitish tongue-shaped mass ; 

 lying immediately beneath b. 



It varies in size and character with the season of 

 the year. (Cf. Sect. G.) 



d. The genital duct. In the male; a highly convoluted 



