28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



basis for all subsequent discussions in this paper on the morphology 

 of the ovipositor. The assumption seems to have ample support from 

 embryology; but, if the plates in question should be shown to be 

 something else than the basal elements of appendages, it will be neces- 

 sary only to change their names ; their relations to structures evolved 

 from them in the Pterygota will not be altered. The abdominal styli 

 of the Thysanura support the abdomen and play an active part in the 

 locomotion of the insect. The writer has elsewhere (1931) discussed 

 the evidence bearing on the morphology of the styli, showing that, 

 while there is much reason for believing that the styli and their homo- 

 logues in various pterygote larvae are the rudimentary telopodites of 

 the abdominal segments, the question cannot be regarded as settled; 

 the styli may be basal epipodites of the appendages, from which the 

 telopodites have entirely disappeared. 



The writer has not been able to make an exact study of the abdom- 

 inal musculature in the Thysanura, but even with poorly preserved 

 specimens it can easily be seen that each stylus-bearing plate of the ab- 

 domen is amply provided with lateral muscles that take their origin on 

 the abdominal terga. In fact, it appears that all the dorsoventral mus- 

 cles of the abdomen in the Machilidae are attached ventrally on 

 the stylus-bearing plates, there being no muscles of any kind con- 

 nected with the small median sternal plates. It would thus seem 

 that in the Thysanura the lateral body musculature of the abdomen 

 is formed entirely of the tergal musculature of the limb bases. In 

 studying the abdomen of pterygote insects the writer (1931) was led 

 to make the statement that no evidence was found suggesting the 

 derivation of the lateral abdominal musculature from the muscles 

 of the limb bases ; and this is true, since in exopterygote larvae that 

 preserve distinct limb base lobes on the abdomen, none of the body 

 muscles is attached directly on the limb bases. The diversification 

 of the muscle attachments in adult Pterygota, in which some of the 

 lateral muscles may be tergopleural and others tergosternal, cannot 

 be taken as evidence of a primitive condition, since it is evidently 

 an adaptation to the mechanism of respiration and of other body 

 movements. Likewise, in endopterygote larvae a secondary specializa- 

 tion in the musculature may obscure the primitive muscle pattern. 

 The condition in the Machilidae, however, is perhaps more significant ; 

 it might be interpreted as indicating a derivation of the lateral body 

 musculature from the primitive leg muscles, though the extreme re- 

 duction of the sterna must be taken into account as a factor bringing 

 about a secondary transposition of some of the body muscles to the 

 expanded limb bases. 



