191)9.] NATURAL, SCIENCES OF PHILADELPHIA. 1 



Lowne, '90, is quite incorrect in his statement that the prothoracic 

 sclerites cannot be homologized with those of the other two segments, as 

 a glance at the thorax of any Blattid would have convinced him. 

 His criticism of Audouin, '20, for taking as a type so "specialized" a 

 segment as the wing-bearing one, is likewise wholly unjustified; for 

 a comparative study can lead to no other conclusion than that the 

 segment bearing the functional wing has undergone the least modifi- 

 cation. The pro thorax in many cases has been reduced to a mere 

 collar, and, indeed, Brongniart, '90, finds that in certain fossil insects 

 this segment bore a wing-like appendage which has since been lost. 

 The prothorax, then, cannot be chosen as a type, and in the segment 

 which does not bear the functional wing — as for example the meta- 

 thorax of the diptera — it is convincingly apparent that there has been 

 a great fusion and reduction of both sclerites and muscles. It is the 

 wing-bearing segment, therefore, that more nearly represents the primi- 

 tive condition, and if Lowne had not confined his attention to a special- 

 ized species of the highly specialized dipteran order, he would have seen 

 how illogical are his conclusions for insects in general, based upon so 

 modified a form. 



General Description. 



The Tergum. — As has been previously stated, the structure of the 

 prothorax is essentially the same as that of the other two segments. 

 This principle, however, may lead to a mistaken interpretation of the 

 condition exhibited in the prothoracic tergum (or the pronotum, as 

 Burmeister, '32, terms it) of certain insects. Thus most text-books 

 state that in the grasshopper's pronotum, the ring-like areas, produced 

 by a series of transverse furrows, represent the prsescutum, scutum, 

 scutellum and postscutellum — as is figured by Brooks, '82, for example. 

 Theoretically this sounds very plausible, but a comparison with a large 

 number of Saltatoria shows that these wrinklings are largely of a 

 secondary nature. Not only is the musculature quite different, but 

 it is likewise the case that the four subdivisions of the meso- and meta- 

 thoracic terga never occur as such regular, parallel rings. In addition 

 to this, in certain Acrididse (Dictyophorus for example) there are even 

 more than four rings, and in some cases the transverse furrows which 

 mark off these rings are interrupted, thus showing their secondary 

 character. 



The praescutum and postscutellum usually form what Kirby, '28, 

 terms a phragma — that is to say an inward projecting process of the 

 tergum. Such a prsescutum or postscutellum has never been described 



