CHAPTER V. 



THE COCKROACH {BLATTA OR/ENTALIS). 



The common Cockroach of our kitchens is the one that is 

 selected as the type for the present chapter ; but an American 

 species, Periplaneta americana, is really a better animal for 

 dissection, as it is larger than the former species, which origi- 

 nally came to us from the East. The inost important difference 

 between the two is, that P. americana is winged in both sexes, 

 while in Blatta orientalis it is only the male which has fully 

 developed wings. 



The cockroach belongs to the same great division of the 

 animal kingdom as does the crayfish. It is an arthropod ; but 

 it breathes by means of tracheae instead of gills, and is referred, 

 on that and other accounts, to a separate division of the 

 Arthropoda, the Tracheata, in which division it is a representa- 

 tive of the class Insecta. 



As in the crayfish, the body is clearly segmented, and the 

 segmentation is more obvious in the abdominal than in the 

 thoracic or cephalic regions. There is a plain division between 

 head and thorax, a narrow " neck " joining and marking the 

 line of division between them. 



It is believed, from a consideration of the appendages, 

 which will be considered presently, that the head consists of 

 three fused segments, lying behind the mouth, and a prostomium, 

 comparable to that of the earthworm, lying in front of it. There 

 are, however, no indications in the sclerites, which form the exo- 

 skeleton of the head, that this is probably the case. The head, 

 which is carried at right angles to the thorax, its appendages 

 lying therefore behind it instead of below it, is covered by a 



