216 SYSTEMATIC ZOOLOGY. 



only be ascertained by the appendages or by the features 

 presented in development. 



Usually these segments can be grouped in regions, of 

 which, at most, three can be distinguished: in front the 

 head; next., the thorax; and behind, the abdomen (fig. 

 48). The head is largely concerned in the taking of food, 



FIG. 48i Diagram of grasshopper showing the body divided into the three 



regions: head, thorax, and abdomen. 



and is usually the seat of the special senses. The thorax 

 is the locomotor region, while in the abdomen the primi- 

 tive segmentation is most marked. 



Through the body as an axis runs the alimentary canal, 

 the mouth being on the under surface of the head, while 

 the vent is at the tip of the abdomen. Above the diges- 

 tive tract lies the heart, which in many forms has a 

 chamber in each of several somites of the body; that is, 

 the heart is segmented. On the floor of the body, below 

 the alimentary canal, is the nervous system, which ex- 

 hibits this segmentation in a more marked degree. In 

 each segment there is a paired enlargement or ganglion 

 from which nerves go to the various organs of the seg- 

 ment. These ganglia of the successive segments are con- 

 nected with each other by a double nerve-cord, so that 

 all are in communication with each other. At the front 

 end of the body one of these nerve-cords passes on one 

 side of the oesophagus, the other on the other, and above 

 it they unite with a large compound ganglion, the so- 

 called brain. In this way a part of the nervous system 



