2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



striking differences among the ventral intersegmental muscles than 

 one would ordinarily expect from members of the same order, not to 

 say genus. Since a precise knowledge of the distribution of the ventral 

 muscles is essential if one is to draw from them conclusions concern- 

 ing thoracic evolution, a reinvestigation of these species was made, 

 in the course of which it became apparent that familiarity with a 

 wider variety of blattids would be helpful. Eventually 19 species 

 were examined. The discussion below attempts to extract from this 

 material information that illuminates certain important facets of the 

 evolution of the thorax in winged insects. 



METHOD AND MATERIAL 



Specimens from culture were etherized, pinned venter-down in a 

 wax dish, and covered with water. Under binoculars, the dorsal 

 integument was carefully cut away from thorax and abdomen, after 

 which the ventral system of muscles was gradually exposed by re- 

 moving structures that interfered with the view. A few details were 

 checked from other angles. Liberal staining with i percent methylene 

 blue from time to time in the course of dissection proved helpful, and 

 brief hardening in 70 percent alcohol was occasionally resorted to. 

 The magnification used was 12.5 to 50 times. At various stages of 

 dissection drawings were made to scale on squared paper with the 

 aid of a micrometer eyepiece. 



P. americana (L.), Blaherus craniifer (Burm.), Blatta orientalis 

 L., Blattella germanica (L.), and Supella supellectilium (Serv.) 

 were available in our laboratory. Cultures of the following species 

 were supplied through the generosity of F. H. Babers, J. H. Fales, 

 W. L. Nutting, L. M. Roth, P. R. Ruck, C. N. Smith, and E. R. 

 Willis: P. oitstraJasiae (L.), P. brunnea Burm., P. fuliginosa 

 (Serv.), Blaherus giganteiis (L.), Blattella vaga (Heb.), Cryptocer- 

 cus piinctulatiis Scud., Diploptera dytiscoides (Serv.), Eurycotis 

 floridana (Walk.), Leucophaca maderae (Fabr.), Nauphoeta cinerea 

 (Oliv.), Ncostylopyga rhomhifolia (Stoll), Parcohlatta pennsylvanica 

 (DeGeer), and Pycnoscelus surinamensis (L.). A single preserved 

 specimen of Maeropmiesthia rhinoceriis Sauss. also was dissected. 

 The 19 species investigated were chosen mainly on the basis of avail- 

 ability and are but a small fraction of the more than 3,500 species of 

 cockroaches that {fide Rehn, 195 1) have been described. 



Nymphs and adults of both sexes were examined for most species, 

 although few differences attributable to stage or sex were found 

 among the msucles to which the present investigation was confined. 

 For comparison, data were obtained from the literature or from the 



