INSECT SPINASTERNAL MUSCULATURE — CIIADWICK I 33 



were probably formed "by the secondary union, end to end, of fibers 

 which initially did not extend beyond the length of one segment." For 

 lack of further evidence, Barlet refrains from any guess as to the 

 probable components. It is noteworthy that these long muscles course 

 ventrad of both the pleuro-endosternal and transverse intersegmental 

 ligaments, a fact that does not facilitate interpretation of how they 

 came into being. Nevertheless, we may accept Barlet's surmise as to 

 their origin as probably correct in principle, the more so since we 

 have seen, in sections 6 and 7 above, other similar examples of the 

 formation of muscles more than one segment in length. One is tempted 

 to seek the missing 2sps-iils, ssps-2ils, etc. (section 9) in the long 

 pleuro-endosternal muscles of Lepisma, but this is pure conjecture 

 that might furthermore meet some topographical difficulties. An em- 

 bryological study of Lepisma would furnish an unexploited oppor- 

 tunity of obtaining evidence on the question. 



c, Spinacoxal muscles: 



11. ISpS-CXi 2$pS-CXt 3SpS-CXs 



12. ISpS-CXt 2SpS-CXs 



II. In some 13 to 15 orders, each spina, with exception of the often 

 missing third, serves as a point of origin for a spinal remoter of the 

 immediately preceding coxa. Serial homologues of these muscles have 

 been found even for the third coxa in 8 or 9 orders, and may be yet 

 more widely represented, as Maki (1938) has suggested, in the defini- 

 tive posterior furcal rotators of some species. Badonnel's (1934) 

 study of the innervation of the corresponding furcocoxal muscles in 

 Stenopsociis tends to support this view. 



It is worth remarking that in Thysanura two separate spinal re- 

 motors are found for each coxa (Barlet, 1954, Nos. pp, 100; no, in; 

 116, 7/7). Maki (1938) noted a double spinal remotor of the first 

 coxa in Lociista (Nos. 25, 26). A somewhat similar situation occurs 

 in all three segments of larval dytiscids (Speyer, 1922; Chadwick, 

 unpublished), where one band originates on the spina or its equivalent 

 while the second originates on the corresponding Us and thus crosses 

 the contralateral homologue on its way to the insertion in the opposite 

 coxa. Larval Corydalus (Megaloptera) also has a cruciate coxal re- 

 motor, as well as the usual spinal remotor, in the second and third 

 segments ; but here the cruciate muscles originate on the respective 

 furcal arms (Chadwick, unpublished). The cruciate muscles are no 

 longer found in the adult of this species or in a North American 

 species of Sialis, but Czihak (1953) lias noted three remotors of the 

 first coxa in Sialis flavilatera L. Two of them {Mm. spino-coxales) 



