114 Sellards — Structure of Paleozoic Cockroaches, 



fication as a result of a specialized arrangement of the repro- 

 ductive parts. A double fold in the ventral integument forms 

 a characteristic genital pouch, bounded in front and above by 

 the eighth and ninth and perhaps a vestige of the tenth sterna, 

 and below by the enlarged seventh. The main function of 

 this pouch is to retain the egg case while the eggs are being 

 placed in it, and in some species during the period of incuba- 

 tion. The ovipositors have become very much reduced and 

 adapted to serve the specialized function of guiding the eggs 

 into the egg case. The terga of both male and female have 

 also become more or less reduced. As will be seen from the 

 present study, the abdomen and ovipositor, as well as the front 

 and hind wings of the paleozoic cockroaches, are in important 

 respects more generalized than in their living descendants. 



Historical Resume. — The cockroaches of the paleozoic have 

 been known heretofore for the most part from the wings only. 

 Being farther removed from the organic juices of the decay- 

 ing body, the wings stand a better chance of preservation, 

 especially the more or less coriaceous and resistant tegmina. 

 The body, on account of the large amount of organic matter 

 present, decays more rapidly, and uo doubt often served as 

 food for the numerous animals inhabiting the water at that 

 time ; hence is much more rarely preserved. The chitinous 

 nature of the wings, on the contrary, renders them compara- 

 tively resistant. Moreover, as suggested in an earlier paper, it 

 is probable that some of the small batrachians, dragon flies, or 

 spiders, found in the same deposits, may have acquired the 

 habit of biting off and rejecting the wings, as do the recent 

 dragon flies, bats, and some arachnids. The detached wings 

 are, moreover, readily carried by currents of water into places 

 where permanent deposits are accumulating. The distinction 

 between the paleozoic and recent forms was originally based 

 almost entirely on differences in the front wings.* Some 

 additional knowledge of the structure of other parts of the 

 body has since accumulated from the studies of a considerable 

 number of investigators, among whom are Scudder, Brongn- 

 iart, Woodward, Deichmuller, G-oldenberg, G-einitz, Germar, 

 and others. After the tegmina, the pronotum is the part of 

 the body most commonly preserved, and has been described in 

 connection with the wings by several authors, especially by 

 Scudder and by Brongniart. The habit of concealing the 

 head beneath the pronotum was evidently already developed 

 in paleozoic time, and it is usually rare that any portion of the 

 head is apparent. Woodward detected parts of the head on 

 Etoblattina Peachii and Leptoblattina exilis, on both of which 



* Scudder, Mem. Boston Soc. Nat. Hist., vol. iii, p. 29, 1879. 



