Fig. 2. 



A BOARD OP AGRICULTURE. 



ternal organs. The nervous system consists of 

 a double nerve-centre or ganglion in the upper 

 part of the head, connected with another below 

 by nerves that pass around the gullet on each 

 side, so as to enclose it as in a ring, and this 

 lower double ganglion is connected by a double 

 nervous cord with a series of similar ganglions 

 or nerve-masses, which are arranged along the 

 lower side of the body, below the intestine, each 

 ganglion sending off small nerves to the adja- 

 cent organs (figure 2). The rings of the body 

 are thickened in certain parts, and in the head 

 and middle region of the body are more or less 

 consolidated. They thus form a somewhat firm 

 external skeleton, composed of 

 a peculiar substance, called 

 chitin. When the rings are 

 movable this outer covering, 

 where it connects the rings to- 

 gether, is thinner and flexible, 

 and often folded inward so as 

 to form peculiar joints. The 

 legs, jaws, and other external 

 organs, are merely hollow out- 

 foldings of the outer covering, 

 and contain, like the body, the 

 muscles that move the various 

 parts, while their cavities com- 

 municate freely with that of 

 the body, and thus receive their 

 supply of blood, nerves, etc. 

 Each joint of the legs and other 

 appendages is also formed by 

 a thinner portion of the outer 

 covering, which is folded in 

 upon itself in various ways. 

 The wings, when present, are 

 also outfoldings of the integu- 



For description of Figures see next page. 



Fig. 1. 



