NO. II THORACIC MUSCLES OF COCKROACHES — CHADWICK 21 



The profurca bears two anteriorly directed longitudinal ventral 

 intersegmental muscles. The stronger, consisting of two or more 

 bands and serially homologous with the muscles jui-fi(2, j'h-f^fs, 

 passes into the head to insert on the tentorium. This muscle, jui-tent 

 (figs. 1-18: i), is commonly considered to be more than one segment 

 in length (Snodgrass, 1935, p. 159). The weaker, usually a thin, flat 

 strap of somewhat degenerate appearance, has a more ventral origin 

 on jui (figs. 4, 5, 9: 2) and is inserted on the mesal lobe of the 

 ipselateral second cervical sclerite. Possibly this site should be re- 

 ferred to the Oils, which are certainly included in the first cervical 

 sclerites, icv, of which the 2cv may be merely subdivisions (Cramp- 

 ton, 1926) ; but this question cannot be settled until the constitution 

 and muscular connections of the various cervical structures of insects 

 are better understood. 



GENERAL DISCUSSION 



Reinvestigation of the ventral intersegmental muscles of the three 

 cockroaches previously studied by others has shown each of the 

 earlier accounts deficient in some respects. The defects are mostly 

 errors of omission. Thus, none of the earlier investigators noted the 

 muscle icv-cxiX or the three postcoxal ligaments lils-fui, etc. That 

 they did not is understandable, for these are hardly muscles in a func- 

 tional sense, even though the cervicocoxal "muscle" does have a con- 

 tractile core a few microns in diameter. Carbonell's (1947) exclusion 

 of the ligament ju3-fu3{=ssps-fus) and of the bands "^sps"-ventr. 

 diaphr. from his description is likely to have been on similar grounds ; 

 for in most other details his depiction of P. americana is accurate 

 and complete. However, unless Maki's (1938) specimens of 

 P. australasiae difi^ered radically from those of this species available 

 to the writer, one must reject Maki's assertions that the muscles 

 isps-fui, isps-cxz, 2sps-fiii, 2sps-cxs, and 2sps-SjiA are absent, and 

 that a muscle, 2ps-fu2, unknown in any other cockroach, is present. 

 Miall and Denny (1886) stated explicitly that they had not given a 

 complete account of the muscles of B. oricntalis, so that there is no 

 cause for surprise in the fact that this species has numerous muscles 

 unmentioned in their description. 



When these few corrections have been made, it is seen that all 

 species of cockroaches thus far studied have nearly identical com- 

 plements of ventral intersegmental muscles. The spinasternal pro- 

 motors of the coxae, isps-cxe and 2sps-cxs, are absent from some 

 species and show signs of weakness in others. The metathoracic post- 



