72 THE COCKROACH [CH. Ill 



imagine what its habits may have been in pre-human 

 periods. 



The indigenous cockroaches, which are referred to 

 below, live in shrubs, under moss, dried leaves, refuse 

 heaps and so forth, and thus indicate the steps by which, 

 in all likelihood, P. orientalis quitting a purely vegetarian 

 diet came to gather up the unconsidered trifles cast out 

 around primitive settlements, and so became intimately 

 associated with man and man's doings. The factors which 

 have contributed to the success of this animal are not far 

 to seek ; in addition to its form and colour already alluded 

 to, it has a fair turn of speed and is difficult to catch, and 

 when caught to hold, for its smooth surface readily slips 

 from the grasp; and further it possesses a most disagreeable 

 smell (and taste ?) which taints everything that it touches, 

 and pervades its accustomed haunts. This evil odour is 

 due to the secretion of a pair of glands situated on the 

 back. They are sunk in the thin membrane which 

 connects the 5th and 6th segments of the abdomen 1 . 

 If a cockroach is caught by quickly putting the hand 

 upon it as it runs over the floor, a sticky glue-like fluid 

 is at once emitted by these glands and gives forth the 

 characteristic odour with great intensity, nor is it at all 

 easy to rid the hand of the taint. There can be little 

 doubt that this quality is a sufficient deterrent to many 

 insectivorous animals, though some few have overcome 

 the dislike. 



The male cockroach when adult possesses a pair of 

 wings beneath the wing-covers by means of which flight 



1 Minchin, Q.J.M.S. xxix. and Zool. Anz. 326, 1890. 



