LOBSTEE OE CEATFISH 153 



ticularly the position of these points. Use an injected 

 specimen if obtainable. 

 Lying beneath the shell look for 



A. The epidermis or " hypodermis."— Do you find 

 it everywhere inside the skeleton? What is its 

 color? Is it more closely attached to the seg- 

 ments of the shell at some points than at others ? 

 If so, where are these points ? 

 Eemove the epidermis. 



B. — The Muscular System. 

 Lying one on each side of the median dorsal line find 



a. The extensor abdominis muscles. — Trace the 



two strands forward to the thorax. What is 

 their color ? Shape ? Where do they arise ? To 

 what are they attached posteriorly ? JSTotice that 

 each is made up of smaller strands, and that 

 these strands are attached to the terga of the 

 segments. Are the two strands connected in 

 any way ? Are the muscle fibres attached to the 

 epidermis or to the exoskeleton? When these 

 muscles contract, what motion do they produce ? 



Eemove the extensor abdominis muscles. 



Arising on the side of the carapace, directly 

 above the origin of the extensor abdominis, are 



b. The levator abdominis muscles.— In what di- 



rection do these muscles run ? To what are their 

 posterior ends fastened? What relation as re- 

 gards position do these muscles bear to a ? How 

 do thejr compare with a in shape and size ? What 

 motion do they produce ? 



c. The flexor abdominis muscle. — The greater 



