28 FIELD ZOOLOGY. 



of the body. But in insects, so far as investigation has 

 shown, the aerating system of air tubes touches the aU- 

 mentary canal only at the region where the Malpighian 

 tubes are liberally supplied with tracheae. In the human 

 body, waste Hberation is accomplished through the lungs 

 (gaseous) and through the kidneys (liquid) . In insects, 

 through the aeration of the Malpighian tubes, that is 

 the kidney region, the two sorts of waste liberation may 

 reinforce each other. As to the remaining waste libera- 

 tion, not accomplished by the Malpighian tubes,_ the fat 

 body of the insect, lying along the alimentary canal and 

 the dorsal heart, also acts as a waste eliminator, and in 

 some insects acts as a storage tract for the deposit of 

 waste ; especially is this true where the insect is a primitive 

 insect and there are no Malpighian tubes. The. blood of 

 insects, which is more like the lymphatic fluid of the 

 human animal, contains many fat globules, indicating a 

 connection between this fat body and the circulation of 

 the blood. 



Nervous System. 



The nervous system of the larva of an insect, if we 

 select an insect having complete metamorphosis, as a 

 butterfly, is a type of a simple nervous system, one 

 nervous ganglion for each segment of the body, joined by 

 a double cord, and lying in the middle line of the body 

 ventrally. As the adult stage is approached, there is 

 more or less of fusing of these ganglia in all the different 

 orders of insects ; but in an adult butterfly the front end 

 of the nerve chain becomes modified into two ganglia, 

 one lying a little forward called the brain or cephalic 

 ganglion, and the other lying a little below the brain and 

 called the subcjesophageal ganglion. The brain supplies 



