Sellards — Structural Characters of Cockroaches. 307 



Art. XXXI. — Some Mew Structural Characters of Paleozoic 

 Cockroaches /* by E. H. Sellards. (With Plates VII and 

 YIIL) 



The relatively large number of cockroaches that have been 

 obtained from rocks of Carboniferous age indicates that these 

 insects were extremely abundant even at that early time. The 

 Paleozoic species, however, have been known heretofore, for 

 the most part, from the wings alone, and of these only the 

 more resistant front wings, or tegmina, are as a rule preserved. 

 The more perishable organic matter of the body no doubt 

 hastens its decay. The wings, on the other hand, are almost 

 devoid of destructible organic matter, and at the same time 

 their strong framework of veins makes them fairly resistant. 

 Various contemporaneous and associated animals, such as small 

 batrachians, spiders, and dragon-flies, doubtless fed then as now 

 upon the bodies of insects, and some of them may have even 

 acquired the well-known habit common to ordinary bats, 

 modern dragon-flies, and some recent spiders, of biting off and 

 rejecting the wings of the insects on which they prey. When 

 detached, the wings are easily carried by currents of water, 

 and are thus readily transported into places where permanent 

 deposits are accumulating. 



The distinctions between Paleozoic and recent cockroaches 

 were originally based almost entirely on the framework of the 

 front wings. f Some additional knowledge of other parts of 

 the body has since been obtained, although acquired slowly, 

 owing to the scarcity of favorably preserved specimens. A 

 good deal of instructive material, however, has now accumu- 

 lated, both from fuller collections from old localities and the 

 discovery of new ones. 



It is almost a decade since the appearance of Professor Scud- 

 der's last important contribution to the knowledge of Paleozoic 

 cockroaches. - In the meantime the interest in early types of 

 insects has been greatly increased through the study of recent 

 forms, and especially through a better understanding of the 

 homologies of the wing veins in the different orders. The 

 common primitive ancestor of all winged insects, or the near- 

 est approach to such a form, is naturally to be sought in 

 Paleozoic rocks. A return to the study of the early representa- 

 tives of the cockroaches in the light of new and rich material 

 seems, therefore, especially opportune at this time. 



The writer has in preparation a study of the structure of 

 Paleozoic cockroaches, including a description of new forms 



* The present paper is for the most part taken from a more extended study 

 of American Paleozoic cockroaches, now in preparation. 



fScudder, Mem. Boston Soc. Nat. Hist., vol. 3, pp. 23-134, 1879. 



Jour. Scl— Fourth Series, Vol. XV, No. 88.— April, 1903. 

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