78 



BEGINNERS' ZOOLOGY 



the front, driving the blood forward. The blood contains 

 bodies corresponding to the wJiite corpuscles of human 

 blood, but lacks the red corpuscles and the red colour. The 

 blood is sent even to the wings. The veins in the wings 

 consist of horny tubes inclosing air tubes surrounded 

 by blood spaces, and the purification of the blood 



takes 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 unequalled 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 the 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 /tearing is variously located in different in- 

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



Fig. 132. — Nervous Sys- 

 tem of Bee. 



Fig. 133.— 



Feeler 

 of a beetle. 



