45 [ 465 ] 



the nerves of relation, because they control the sensations and motions 

 which associate the animal with the world around it. But in addition 

 to these, there have been discovered a number of very fine nervous fila- 

 ments proceeding? from the brain, and extending down into the body, 

 and fiu-nished with minute ganglia of their own, which are supposed to 

 represent the symimthetic sj'stem of nerves which preside over the in- 

 ternal functions, such as those of digestion and secretion. 



The foregoing cut represents the nervous system of a butterfly, {Papilio 

 hrasslcce) (after Herold), A exhibiting that of the larva, B that of the 

 pupa, and c that of the perfect insect ; and showing how the nervous 

 system becomes shortened^and consolidated in changing from the lower 

 to the higher stages. Fig. d shows the more concentrated nervous sys- 

 tem of a Coleopterous insect, as exhibited in the common English Cock- 

 chafer or Door -beetle, Melolontha vuJgarns ; (copied from Straus^) 



THE CIRCULATORY, OR SANGUIFEROUS SYSTEM. 



The blood of insects is a colorless fluid which does not circulate in 

 closed vessels or tubes, like that of the higher animals, but permeates 

 the tissues of the body. The only vessel that can be discovered, is an 

 oblong, membraneous, pulsating sac, situated in the upper or dorsal 

 part of the body, and which evidently represents the heart. This is 

 divided into several comi^artments by cross-valves which are so ar- 

 ranged as to permit the blood to i)ass only in a forward direction. The 

 heart is prolonged anteriorly into a narrower tube analagous to the 

 aorta. Through this the blood flows first towards the head, and thence 

 through the body, returning to the heart which it enters through open- 

 ings at its sides. As compared with that of the w^arm-blooded ani- 

 mals, the blood of insects is not only colorless, but small in quantity, 

 and must circidate very slowly, as is proved by the fact that when their 

 bodies are wounded no blood escapes. 



THE RESPIRATORY SYSTEM. 



Most of the organs of insects, and their functions, ha\e an obvious 

 analogy to those of the higher animals, but their breathing apparatus 

 is constructed upon_ an entirely different plan. In all the vertebrated 

 animals the blood is carried in vessels to a particular part or organ of 

 the body, for the purpose of being exposed to the life-giving influence 

 of the air. This part, in terrestial animals, is the lungs, and in aquatic 

 animals, the gills. But in insects the process is reversed, and the air is 

 carried to the blood by being distributed to every part of the body in 

 very delicate pearl-white tubes or vessels, which present a beautiful ap- 

 pearance under the microscope. They are called trachea, or air tubes. 

 They admit the air through little openings ^along the sides of the in- 



