86 thb ebb-kebper's guidb ; 



fluid, in all normal conditions, and contains not the organs 

 themselves, or any part of them, but only the elements, which 

 are absorbed by the tissue and converted into the organs, or, 

 to be scientific, are assimilated. The blood of insects is nearly 

 destitute of discs, having only white corpuscles. The white 

 corpuscles are called leucocytes. They are now known to act 

 as so many animals, and are powerful for good in destroying 

 microbes. We thus call them phagocytes. These phagocytes, 

 in insect transformations, remove, we may say eat up, the no 

 longer useful organs. It is this way that a tadpole's tail is 



Fig. 34. 



Croas ^ectlo/i of J^ee, after Cheshire. 



li Heart. Tr. Tracheae. 



,S7. Stomach. ga Ganglion. 



d Diaphragm. 



removed. This process is known as phagocytosis. The leu- 

 cocytes are also found in the digested food, and like the same 

 in higher animals, are amoeboid. Schonfeld has shown that 

 the blood, chyle, the digested food, and larval food, are much 

 the same. 



The respiratory or breathing system of insects consists of 

 a very complicated system of air-tubes (Fig. 1, 27). These 

 tubes (Fig. 35), which are constantly branching, and almost 

 infinite in number, are very peculiar in their structure. They 

 are composed of a spiral thread, and thus resemble a hollow 

 cylinder formed by closely winding a fine wire spirally about a 

 rod, so as to cover it, and then withdrawing the latter, leaving 



