NO. im. NORTH AMERICAN THYSANOPTERA— HINDS. 99 



Ta?\s>/s. — This is the most distinctive part of the leg. As a rule it 

 is composed of two segments, though in larvw and the fore tarsi of 

 many species but one is present. The division between the two is 

 oblique so that the under surface of the first segment is longer than the 

 upper. Both segments are more or less cylindrical. The last segment 

 termintites in a cup-shaped or hoof -like end which has been mistaken 

 sometimes for a third tarsal segment. Upon the inner side of the fore 

 tarsi are found structures which are nearly always characteristic of 

 famiUes. The ^l^^olothripida^, in both sexes and it is stated also in the 

 pupal stage, bear upon the tarsus a peculiar hook-like structure the 

 function of which is not understood. (See Plate I, fig. 9.) The finger- 

 like hook is bent back upon itself, pointing toward the base of the 

 tarsus and almost touches the point of a short, stout spine standing 

 erect at its tip. In many species of Phloeothripida?, though not in 

 all, there is on the inner side of the tarsus a more or less stout tooth 

 which stands nearh^ erect and is slightly recurved at its tip, and when 

 this tooth is strongly developed, the tarsus, so far as is known, has 

 only one segment. The development of this tooth seems also to be in 

 proportion to the degree of development of the fore femur and its 

 function appears to be to act as a hook in giving a firm hold and thus, 

 assisting the little creature in crawling through small places. Some 

 Phlcjeothripid* show no traces of such a tooth and all grades of develop- 

 ment can be found in different members of this familj-. Both sexes 

 usualh^ possess such a tooth, though that of the male is sometimes 

 much stouter than that of the female. In the Thripid^e the tarsi are 

 simple, without either of these structures in nearly all species, only a 

 few having a small tooth. 



The tarsi are usually said to be clawless, but I do not consider this to 

 be always the case, for some species have one and some two distinct, 

 apparentl}' movable claws on the sides near the end. ■ 



Sjnnes. — Each segment of the leg may bear numerous spines, and 

 some of these may be particularly well developed and worthy of note. 

 In many Tubulifera there is upon the inner and lower side of the 

 femur near its base a slender spine very much longer than any of the 

 others. The hind tibia in most species of Thri]3id8e is furnished with 

 a row of ^stout spines along the inner side and in man}" species a pair 

 of similarly stout spines is borne at the tip of each tibia. Other 

 specialized spines are sometimes found. 



Bladdci'. — This structure, so remarkable and characteristic as to 

 suggest the name Physopoda for the order, is protrusile from the end 

 of the last tarsal segment. It is found in all species and in both adults 

 and young, but its structure and action does not ^eem to be quite the 

 same in the mature and immature stages. 



As has been said, the end of the adult tarsus is cup-shaped. The 

 wall of the cup is firm and in some parts, especially the underside, 



