38 GENERAL ZOOLOGY 



Man is indebted to some of these insects for a variety of 

 products of greater or less value. One of the scale insects 

 (Coc'cus cac'ti), found on the cactus in Mexico, is the source 

 of the red coloring matter, cochineal ; to another {Tachar'- 

 dia lac'ca), of India, we are indebted for shellac. The manna 

 mentioned in the Book of Exodus is probably the secretion 

 of a scale insect. It is a sweet substance used today by the 

 Arabs as food. 



Definition of Homoptera (Gr. homo-, "like"; pteron, 

 "wing"). The insects belonging to the Homoptera have 

 mouth parts modified as a sucking beak. In most instances 

 (except in the case of scale insects) there are two pairs of 

 membranous wings arranged as a sloping roof over the back. 

 Since the nymphs develop directly into the adults, the 

 Homoptera have incomplete metamorphosis. 



