7* 



ANIMAL BIOLOGY 



the front, driving the blood forward. The blood contains 

 bodies corresponding to the white corpuscles of human blood, 

 but lacks the red corpuscles and the red color. The blood 

 is sent even to the wings. The ribs on the wings consist of 

 blood tubes inclosed in air tubes, so that the blood vessels 

 are surrounded by air, and the purification of the blood is 



taking place throughout the course 

 of the circulation. Hence the im- 

 perfect circulation is no disadvan- 

 tage. The perfect provision for 

 supplying oxygen explains the 

 remarkable activity of which in- 

 sects are capable and their great 

 strength, which, considering their 

 size, is unequaled by any other 

 animals. 



The Nervous System. — The 

 heart in backboned animals, e.g. 

 man, is ventral and the chief nerve trunk is dorsal. As 

 already stated, the heart of an insect is dorsal ; its chief 

 nerve chain, consisting of a double row of ganglia, is near 

 the ventral surface (Fig. 131). All the ganglia are below 

 the food tube except the first pair in the head, which are 

 above the gullet. This pair may be said to 

 correspond somewhat to the brain of backboned 

 animals ; the nerves from the eyes and feelers 

 lead to it. With social insects, as bees and 

 ants, it is large and complex (Fig. 132). In a 

 typical insect they are the largest ganglia. 



The Senses. — ■ The sense of smell of most in- 

 sects is believed to be located in the feelers. 

 The organ of hearing is variously located in different in- 

 sects. Where is it in the grasshopper ? The organs of 



Fig. 132. — Nervous Sys- 

 1 em of Bee. 



