90 PROnEEDTNGS OF THE NATIONAL MUSEUM. vol. xxvi. 



these families certain .spines seem to hav^e undergone much modifica- 

 tion and to have become specialized as sense organs of some particular 

 sort, (See Plate XI, fi^s. 123, 124.) The}- are larger than the unspe- 

 cialized spines, thin walled and aliuost transparent, and usually end in 

 a l)lunt point. In some species they are (piite prominent, l)ut as a rule 

 are inconspicuous and require a careful adjustment of the light to be 

 clearly seen. They are always simple in Phl(eothripidt\> and are 

 usually borne upon segments three to live, sometimes three to seven. 



In the Thripida^ similar structures are found, but they have under- I 

 gone even greater specialization in most cases. In a few genera 

 {ChlrotJvrlps^ Ltniothrlps^ ^i/)finofhrljJs, and J \(rfhc?wt/irij).'^) they are 

 simple and stand singl}'-, one to a segment, upon the outer angles of 

 segments three, four, and sometimes five, and upon the inner side at 

 about the middle of six. In most cases, however, it appears that two 

 of these specialized spines have approached and luiited at their base, 

 so that we find upon the upper side of segment three and the under J 

 side of four, near their tips, a peculiar cresceutic organ having the " 

 same apparent structure as the specialized spines just described and 

 borne upon a small stalk standing in a clear, membranous area. (Plate 

 XI, fig. 123.) In some cases these organs are shaped much like the 

 horns of cattle and are curved in two directions, being curved forward 

 and also toward the axis of the antenna. The fifth segment sometimes 

 bears a simple spine and another one is also well developed upon the 

 innei- side of the sixth. The function of these structures is uncertain, 

 but they are usually called sense cones. 



In the ^^^^olothripida) an entirely different tj'pe of sense organ is _ 

 found, though the two may possibW have much the same function. I 

 Upon the underside of segments three and four are narrow, nmch 

 elongated longitudinally, thin, membranous areas, situated upon the 

 outer half of each segment and a very small round spot of similar 

 structure is similarly placed near the tip of segment five. (Plate XI, 

 fig. 122.) These membranous areas strongly suggest an auditory 

 function, but this is, perhaps, only a possibility. 



Al)normal antennte are not uncommon, and one or both may be 

 deformed. The most common variation is in the line of a reduction 

 in the number of segments through the fusion of two or more of the 

 apical ones. Such deformed antenna? may not be shorter than the 

 normal ones, but there is usuall}' some reduction in length. In one 

 case, at least {Aptinothrips Tufus var. connatticornis)^ there occurs a 

 regular and apparently normal fusion of the two segments constitut- 

 ing the style of the typical form with the sixth segment (Plate V, figs. 

 52, 54), which in this case is considered as a varietal distinction. An 

 increase in the number of segments above the normal, by a division of 

 one or more, is not known. 



The antennie are carried extended forward in front of the head, and 



