108 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxm 



plainl}^ visible through the body of the insect. It is composed of four 

 distinct plates or valves, two of which, forming the under or anterior 

 pair, are attached to the very narrow ventral plate of the eighth seg- 

 ment and two, forming the upper or posterior pair, are attached to the 

 sides of the ventrally extended dorsal plate of the ninth segment. The 

 ovipositor as a whole is curved either upward (^-Eolothripidjv) or down- 

 ward (Thripidffi) and terminates in a very slender, sharp point. The 

 valves lie verj'^ closel}^ together, but their inner surfaces are g■roo^'od, 

 forming a passagewa}'^ for the egg. The two plates on each side are 

 fitted together in such a wa}^ as to slide back and forth upon each other 

 without being displaced. The upper edge of , the lower plate is grooved 

 and into this groove fits a ridge or tongue formed by the lower edge 

 of the upper plate. The upper edge of the upper plate, except at its 

 base, is fitted with sharp, saw-like teeth pointing toward the base of the 

 valve. The lower plate is provided with similar teeth on the under 

 side of its distal third, while the middle third bears a number of pecu- 

 liar, broad-cutting teeth. The ovipositor is movably connected with 

 the abdomen by a number of small supporting plates or levers which 

 also assist in its manipulation. 



In at least two species of Thripidte known to me, the ovipositor docs 

 not appear to be functional though it is plainl}^ present {Chirothrijjs 

 ohesus and ThrijJS j.^er_plexus). 



When not in use, the ovipositor is drawn up close to the bod}" and 

 is received into, and entirelv enveloped b}% a membranous sheath 

 along the last two segments which is made possible bj^ the absence of 

 the ventral plates at this place. The sexual opening is between the 

 eighth and ninth segments in all Terebrantian females. 



As a rule the conical form of the tip of the abdomen also indicates a 

 female. In many of the light colored species, just in front of the base 

 of the ovipositor, is a plainly visible internal organ which has some- 

 times been called the seminal receptacle. It usually appears as a 

 small spherical or rounded body of an orange or brownish color, 

 agreeing closely in this respect with the color of the spermaries of the 

 males in species where males are known. This organ presents the 

 same appearance, however, in certainl}^ unfertilized females of bisexual 

 species, and it is also always present, having the same size and color 

 in several species known to me in which the males are extremely rare 

 or possibly wanting altogether. Certainly a seminal receptacle can not 

 l)e functional in parthenogenetic species, yet I have found this organ 

 constantl}" present through eight or ten generations of a species bred 

 in the laborator^^ where males were never produced. 



Ifale. — Males are, as a rule, considerably smaller than the females. 

 The abdomen is usually bluntly rounded at the end instead of sharply 

 conical, tliough a few species resemble the females in this respect. 

 The stoutest spines are usualh^ at the sides of the ninth segment. In 



