88 LOWER PTERYCOTA 



fringe-winged forms, a characteristic structure. x\nother 

 character almost equally distinctive is found in an aborted 

 tarsal joint modified into a bladder-like expansion of the 

 tarsus. This joint is evidently a modification from the 

 ordinary form with claws. Bladder-foot is one term applied 

 to this group and Physopoda is the name given in some text- 

 books, based on this particular structure. 



The life history of the group in general is rather sim])le. 

 The adults deposit eggs at dift'erent periods through the 

 summer, the generations being somewhat irregular, often 

 three or four in a summer. The eggs are rather large for 

 the size of the insect and somewhat ovoidal or oblong in 

 shape, almost transparent. They are deposited on the 

 foliage or bloom of plants, and hatch quite promptly. The 

 larv?e develop gradually by successive moults, without 

 any striking metamorphosis, until they reach the adult 

 stage when wings are developed. Between the larval and 

 adult stages is a stage of quiescence; parts, including the 

 antennae and legs, are almost immovable. This may be 

 looked upon as a development along the line of the more 

 striking metamorphosis in other cases. The eggs are 

 deposited by means of an o\ipositor that differs in the two 

 subgroups of the family. In one case there is a saw-like 

 ovipositor with blades that glide on each other and enable 

 them to push eggs into soft tissues. In the other division 

 the ovipositor consists of the elongated tubular abdominal 

 segments. The latter is a more simple condition, but the 

 former is more primiti\e. The latter probably results from 

 reduction, the saw-like structure being lost. The dift'erence 

 in egg deposition amounts simply to position in which 

 eggs are laid: in the first instance they are laid more or less 

 within the tissue, in the second instance on the surface. 



For the first group, Terebrantia, the common Thripidse 

 occur in clover, Compositce, apple blossoms, milkweed, etc., 

 also in wheat blossoms. The food plant is determined simply 

 by the flowering season. The most abundant is the wheat 

 thrips, Thrips tritici; this is an economic species, causing 

 some damage. 



