270 



SYSTEMATIC ZOOLOGY. 



these torments. The best is, possibly, the pouring of 

 kerosene upon the surface of all stagnant water. This 



FIG. 89. Larva (a) and pupa (6) of mosquito. 



will kill the eggs as they are laid, while it also destroys the 

 perfect insects as they come from the water. 



SUMMARY OF IMPORTANT FACTS. 



1. The ARTHROPODA share with the Annelids a marked 

 external and internal segmentation, expressed externally 

 by the ringing of the body and the distribution of the 

 appendages; internally by the chambering of the heart, 

 the distribution of the ganglia, and, so far as they are 

 present, by the arrangement of the trachese. 



2. They are distinguished from the Annelids by the 

 presence of jointed appendages, a pair to a somite, as well 

 as by the unequal development of the somites, and by the 

 grouping of the somites in regions. 



3. Three regions may be distinguished: a head with the 

 parts concerned in sensation and the taking of food; a 

 thorax, concerned in locomotion; and an abdomen, in 

 which the primitive segmentation is most perfectly re- 

 tained. 



