52 



The muscular system. — In a fresh specimen the mus- 

 cles appear soft and translucent ; but in specimens that have 

 been kept for a considerable time in a preservative fluid, 

 they are firm and opaque. The greater number of the mus- 

 cles are attached to the ental surface of the body-wall where 

 they form several layers. This is well shown in the abdo- 

 men, where most of the muscles are for moving the seg- 

 ments of the body. In the head and thorax, there are 

 numerous muscles for moving the appendages of the body, 

 and their arrangement is much more complicated. 



To attempt to make a detailed study of the muscular sys- 

 tem would require much more time than can be devoted to 

 this system in this elementary course. Only the more gen- 

 eral features of the structure of the muscles and of their 

 arrangement will be noticed. 



Note that the muscular system is composed of an im- 

 mense number of distinct, isolated, straight fibers, which are 

 not enclosed in tendinous sheaths as they are with verte- 

 brates. 



Mount a few of these fibers in glycerine, and study them 

 with a high power of the microscope. Note that the fibers 

 present numerous, transverse striations, like the striped mus- 

 cles of vertebrates. 



Make a figure of a muscular fiber. 



In this outline each series or layer of closely parallel 

 fibers is considered as a separate muscle rather than an 

 aggregation of muscles. It complicates the subject unduly 

 to consider each distinct fiber a distinct muscle as has been 

 done by some writers. Thus Lyonet in his " Traits Ana- 

 tomique de la Chenille, que range le bois de saiile " describes 

 1,647 muscles without including the muscles contained in the 

 viscera or those contained in the head. 



Take a larva of Corydalis, which has been opened on the 

 ventral side and from which the alimentary canal and the 



