I04 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



and the plate m move in opposite directions. The muscles of the 

 first valvifers, however, must also produce independent back-and- 

 forth movements of the first valvulae when the tip of the ovipositor 

 is inserted into the bark of a tree. The broad, strongly serrate 

 extremities of these valvulae (fig. 31 C) indicate that they play an 

 important part in cutting out the egg chamber, and furthermore, 

 the ends of the outer valvulae are often found in freshly killed speci- 

 mens to be in different positions on the apex of the median shaft 

 formed of the united inner valvulae, indicating that the outer val- 

 vulae are protracted alternately on the ridges of the median shaft (D) . 



The great size of the muscles of the second valvifers (fig. 34, 

 6, 7), particularly of the posterior muscles (7), leaves little doubt 

 that the median shaft of the ovipositor, formed of the solidly united 

 second valvulae, with its strong, sharp spearheadlike tip (fig. 31 C, 

 2VI), is an important piercing implement of the egg-laying apparatus. 

 Because of the union of the second valvulae, the corresponding mus- 

 cles of the second valvifers on opposite sides probably work in unison. 



The mechanism of the ovipositor of any insect could not accom- 

 plish the results it does if the parts of the organ were rigid. The 

 valvulae slide lengthwise upon one another by the movement of the 

 valvifers because they are pliable, and because of the flexibility of 

 their basal connections. A wooden model of the cicada's ovipositor, 

 for example, could not be made to do anything more than to move 

 the shaft up and down at its base. The writer has elsewhere (1921) 

 described the method by which the female 17-year cicada excavates 

 the egg cavities in the twigs of trees in which she deposits her eggs. 



Since the Hemiptera are in some respects one of the most highly 

 specialized and individualized orders of insects, it is somewhat sur- 

 prising that the ovipositor should be more generalized in its structure 

 than in either the Orthoptera or the Hymenoptera. The only orders 

 of insects that seem to approach the Hemiptera in the structure of the 

 head and mouth parts are the Corrodentia and the Thysanoptera. 

 Most of the Corrodentia have a small, simple ovipositor, but in some 

 forms the organ is reduced or absent. Qiapman (1930) says, " In 

 Psocus, Peripsocus, and certain other genera, a distinct if not long 

 and strongly chitinized ovipositor is present. It is composed of three 

 pairs of gonapophyses, one pair arising from the eighth segment 

 and two pairs from the ninth." In Ectopsocus parvuhis, as described 

 by Weber (1931), there are three pairs of small, soft processes 

 surrounding the female gonopore, which appear to represent the 

 three pairs of valvulae, since one pair arises on the eighth segment 



