COCKROACHES 



237 



displacing Stilopyga orientaiis. In addition to these, Rhyparobia 

 r niademe and species of the genus 

 Blalera 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 Blcibera of the natural B 

 size : the species in this genus 

 are extremely similar to one an- 

 other. Blaberae are known in 

 the West Indies as drummers, it 

 being supposed that they make a FlG 132 .n^ r organs of Bmera sp . 

 noise at night, 1 but details in con- A, tegmen ; B, wing. 



firmation of this statement are wanting. 



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 orientaiis, 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 orientaiis. 



Although much work has been done on the embryology of 

 Blattidae, the subject is still very incomplete. The recent memoirs 

 of Cholodkovsky 2 011 Phyllodromia germanica contain so much of 

 general interest as to the development of the external parts of the 

 body that we may briefly allude to them. The earliest appearance 

 of segmentation appears to be due to the centralisation of numerous 



1 Westwood, Modern Class. Insects, i. 1839, p. 418. 

 - Zeitschr. wiss. Zool. xlviii. 1889, p. 89; and Mem. Ac. St. Petersb. xxxviii. Xo. 5, 1891. 



