100 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



strongly chitinized. Into the mouth of this cup is fitted a very deli- 

 cate, protrusile, membranous lobe or bladder. When the foot is 

 raised or at rest, the bladder is wholly withdrawn into the end segment 

 and becomes invisible, as is the case in a majority of mounted speci- 

 mens. The end of the tarsus is now blunt and flat and often seems to 

 be minutel}^ haired. The bladder is, however, always protruded and 

 brought into action when the tarsus is put down or brought into con- 

 tact with an object. The membrane is then pushed out and forin.s a 

 lobe, larger in man}' cases than the cup portion which had previously 

 wholly contained it. The mechanism of this complicated structure is 

 very interesting but difficult to stud3^ It has, however, been worked 

 out, partially at least, by both Jordan and Uzel. The following para- 

 graph on this point is gathered from Jordan's description and my 

 own observations: 



Bladder mecJumism. — A strong ' chitinous rod, attached to muscles 

 in the tibia, runs out through the tarsus and ends in the broadened, 

 heavily chitinized under surface of the cup. The end of the plate is 

 drawn out into weak cords running to the outer parts of the cup wall. 

 Opposite the chitinous rod lies a double fork provided with a joint. 

 The fork is cut short at a chitinous rod lying in the terminal seg- 

 ment of the tarsus and is movably joined thereto. Both arms of the 

 fork are connected with the chitinous rod at their base by a tendon. 

 Between the fork and the terminal plate of the chitinous rod the wall 

 of the cup is usually thin and quite transparent, but in Phloeothripidfe 

 especially it is quite strongly chitinized and opaque. Looking down 

 upon a foot that is inactive (bladder retracted) so that the chitinous 

 rod lies along its middle line, the end appears more or less pear-shaped 

 and small. Upon the surface lies the terminal enlargement of the 

 rod, while the double fork occupies the sides. Between the tips of 

 the fork the extremity appears folded in toward the middle. When 

 the foot is brought into action the chitinous rod is drawii back some- 

 what, so that the attached fork is erected and spread out. The i^revi- 

 ously invisible bladder is now thrust out from the end of the tarsus. 

 The ends of the fork and the chitinous rod continue into the bladder 

 wall as fine rays. The bladder is elastic and ver}" mobile, easil}' ac- 

 commodating its shape to the surface upon which it rests. Looking at 

 a larval tarsus from the side, the chitinous rod is seen to run obliquely 

 from the middle of the tibia to the under wall of the cup. Here it 

 appears to end suddenly without being broadened into a plate as in 

 the adult; still the end of the rod is continued into the wall of the cup 

 as tine rays. The dorsal part of the cup is occupied by a curved claw, 

 the basal part of which is attached to a sort of bracket-like thickening 

 of the wall of that part of the end segment at the base of the cup. 

 Furthermore, the base of the claw is united to the chitinous rod by a 

 sinew, and above the extremity of the claw the tarsus is drawn out 

 into a membranous, longitudinall}' folded lobe. W^hen viewed from 



