THE LOWER ORDERS 



39 



known. Those of the common species that attack man 

 and domestic animals are known to feed on minute par- 

 ticles of organic matter in the dust in the cracks in floors 

 and in other similar situations, even in the dust on the 

 ground, where it is protected from moisture. Fleas have 

 recently been proven to be active agents in the spread 

 of diseases, notably the Bubonic plague, which is carried 

 by the rat-flea. 



34. Physopoda. Thrips. Many writers give the name 

 Thysanoptera to this order, but we prefer the name used 



FIG. 26. Tobacco Thrips, Adult and Nymphs (Physopoda). After 

 Howard, U. S. Dept. Agr. Highly magnified. 



here because of the confusion that may result from the 

 use of a name so much like Thysanura. 



The Thrips are very small insects with narrow wings 

 fringed with long hairs. The 

 mouth-parts are not strongly 

 developed, but are fitted for 

 chewing the softer plant tis- 

 sues, and, to a certain extent, 

 for sucking the sap from them. 

 The development is direct. 

 These insects are usually not 

 numerous and even when abundant are not often ob- 

 served on account of their very small size, most forms 



FIG. 27. Rose Thrips (Physo- 

 poda). Greatly enlarged. 



