It has been increasing in numbers in Vienna, where, according to Brunner, it is {237}displacing _Stilopyga orientalis_. In addition to these, _Rhyparobia maderae_ and species of the genus _Blabera_ have been met with in our docks, and are possibly always to be found there. They are Insects of much larger size than those we have mentioned. We figure the alar organs of one of these species of _Blabera_ of the natural size: the species in this genus are extremely similar to one another. Blaberae are known in the West Indies as drummers, it being supposed that they make a noise at night,[164] but details in confirmation of this statement are wanting. [Illustration: FIG. 132.—Alar organs of _Blabera_ sp. A, tegmen; B, wing.] It is a remarkable fact that no satisfactory reasons can be assigned for the prevalence of one rather than another of these domestic cockroaches in particular localities. It does not seem to depend at all on size, or on the period of development, for the three species _Stilopyga orientalis_, _Periplaneta americana_, and _Phyllodromia germanica_, which are the most abundant, differ much in these respects, and replace one another in particular localities, so that it does not appear that any one is gaining a permanent or widespread superiority as compared with another. There are, however, no sufficient records on these points, and further investigation may reveal facts of which we are at present ignorant, and which will throw some light on this subject. We may remark that Mr. Brindley has found it more difficult to obtain hatching of the young from the egg-capsules of _Periplaneta americana_ and _Phyllodromia germanica_ at Cambridge, than from those of _Stilopyga orientalis_.