COCKROACHES 



221 



become naturalised in various parts of the world in the houses of 

 man. One such species is abundant in Britain, and is the 

 " black beetle " of popular language ; the use of the word beetle 

 in connexion with cockroaches is, however, entomologically in- 

 correct. One or two members of the family are also well known, 

 owing to their being used as the " corpora vilia " for students 

 commencing anatomical investigation of the Arthropoda ; for this 

 purpose they are recommended by their comparatively large size 

 and the ease with which an abundant supply of specimens may 

 always be procured, but it must be admitted that in some respects 

 they give but a poor idea of Insect-structure, and that to some 

 persons they are very repulsive. 



The inflexed position of the head is one of the most character- 

 istic features of the Blattidae ; in activity it is partially released 

 from this posture, but the mouth does not appear to be capable 

 of the full extension forwards that 

 is found in other Insects that inflex 

 the head in repose. The labium 

 is deeply divided, the lingua forms 

 a large lobe reposing on the cleft. 

 The maxillary palpi have two basal 

 short joints, and three longer 

 joints beyond these ; the labial 

 palps consist of three joints of 

 moderate length. The under - 

 surface of the head is formed in 

 large part by the submentimi, 

 which extends back to the occipital 

 foramen. 



The front of the head is the 

 aspect that in repose looks directly 

 downwards ; the larger part of it 

 is formed by the clypeus, which is 

 separated from the epicranium 

 by a very fine suture angulate 



in the middle ; there is a large many-facetted eye on each 

 side ; near to the eye a circular space serves for the inser- 

 tion of the antenna ; close to this and to the eye there 

 is a peculiar small area of paler colour, frequently membranous, 

 called the fenestra, and which in the males of Corydia and 



FIG. 119. Under-surface of Peri- 

 2>laneta australasiae. c, Coxae. 



