6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



exceptions do not discredit evidence supported by a long series of 

 uniform interrelations between muscles and skeletal parts. However, 

 a mere discussion of the matter is useless, and in a final analysis the 

 identities of muscles must be established by a study of the muscle 

 innervation. But, in the meantime, practical results may serve as a 

 basis of judgment. The results of the studies to be given in the fol- 

 lowing pages will appear principally in Part II of this paper, which 

 will attempt to analyze the organs of oviposition, and especially the 

 male organs of copulation, according to the light thrown on the homol- 

 ogies of their parts by an examination of their musculature. The 

 muscles furnish a means as yet but little used for identifying corre- 

 sponding structures in the male genital apparatus of the various orders, 

 and it will be found that they at least give something definite as a 

 working basis in a comparative study of the genitalia. 



For most of the identified material on which the present paper is 

 based the writer is indebted to specialists in the United States Na- 

 tional Museum, including the entomologists of the Bureau of En- 

 tomology, Department of Agriculture, and Dr. Waldo L. Schmitt 

 and his associates, of the Museum's Division of Marine Invertebrates. 

 Specimens of Hcterojapyx and Nesovnachilis, however, were obtamed 

 through the interest of Dr. R. J. Tillyard of Australia. Furthermore, 

 much valuable criticism and information has been contributed by 

 Dr. A. G. Boving, Mr. Carl Heinrich, Dr. H. E. Ewing, and other 

 Museum entomologists of the Bureau of Entomology. 



I. THE ABDOMINAL SCLEROTIZATION 



For purposes of morphological description it is necessary to dis- 

 tinguish regions of the body wall from the sclerites that may partly 

 or entirely occupy the regional areas. Considering the body as a whole, 

 there are two principal surface regions, one including the back and 

 sides above the limb bases, the other the under surface between the 

 limb bases. The first is the dorsum (fig. i A, D) ; the second is the 

 venter (V). Then, in a metameric animal, each somite is likewise 

 divided into a segmental dorsum and a segmental venter. Separating 

 the dorsum and venter of each segment are the latero-ventral limb 

 bases {LB, LB). The regions of the limb bases may be termed the 

 pleural areas of the segments. The free distal part of any limb, mova- 

 ble in a vertical plane on the basis, is the telopodite (Tlpd). 



It is now well understood that the hardened areas, or sclerites, of the 

 body wall of insects, as well as of other arthropods, are not " chitin- 

 ized " or " strongly chitinized " regions, but that they are areas of 



