THE COMMON COCKROACH 123 



be very numerous, and it is highly probable that great 

 numbers of them would never reach maturity at all. 

 Be that as it may, their swarms are still quite large 

 enough for human comfort. Further observations on 

 their life-history, however, are much to be desired, 

 though no doubt difficult to carry out. A closely allied 

 species, Blatta germanica, was studied by Hummel with 

 a very different result, the generations being found to 

 succeed one another with much greater rapidity, and 

 analogy suggests that P. orientalis, which is similarly 

 an active, surface-living insect, should run a similar 

 course, and should, at any rate, complete its cycle of 

 changes more rapidly than sluggish grubs which live in 

 solitariness and concealment. 



When a cockroach is about to moult, the hard skin 

 splits along the back just behind the head, the split 

 gradually extending throughout the length of the three 

 thoracic segments, and through the opening thus made, 

 the insect slowly and with much exertion extricates 

 itself from its old covering, drawing even its legs and 

 its long tapering whip-like antennae out of their sheaths, 

 and also leaving behind in the discarded shell parts of 

 its internal anatomy in the shape of the linings of some 

 of its respiratory tubes. The cast skin, which, when 

 thus left, remains clinging to its support just as when 

 the insect was in it, is usually so perfect, except for the 

 slit along the back, that at a distance it might easily be 

 mistaken for a living specimen. Fig. 35 represents the 

 cast skin of a specimen, which, somewhat unusually, 

 performed its moult, fully exposed, half way up the wall 

 of a room where it had been resting for some time in 

 anticipation of the change. Immediately after the moult 

 the insects are of a creamy-white colour, but after the 

 lapse of three or four hours, if exposed to air and 



