232 M. E. Haase on the 



the chitinous plates, which may be recognized as the remains 

 of the ninth ventral plate on each side of the short gonapo- 

 physial buds. In mature females (with wing-rudiments) the 

 styles have entirely disappeared ; thus they are probably cast 

 off suddenly during a change of skin without being again 

 produced, as no rudiments of them can be recognized. 



In the mature males of Periplaneta, as in those of most 

 exotic genera, the styles persist distinctly and symmetrically 

 developed. 



A want of symmetry in the ninth ventral plate already 

 noticed by Brunner *, probably set up in the males of all 

 forms with the completion of sexual maturity, consisting in a 

 defect of the margin on one side, and an oblique inflection 

 towards the dorsal surface, and probably to be ascribed to the 

 strong development and projection of the long unciform 

 titillator, often causes the reduction, but rarely the complete 

 disappearance, of the styles. Thus in the adult male of the 

 House-cockroach the styles occur only as small knobs, of 

 which the larger left-hand one passes over about in the middle 

 of the ventral plate, which is rendered unsymmetrical by a 

 left-sided emargination ; in Ectobia the right-hand style 

 disappears entirely. These styles, although noticed by 

 Brunner (/. c. p. 129), were entirely overlooked by Brehm j" 

 in Periplaneta. In many exotic genera the styles are quite 

 rudimentary, as in the above-mentioned Panesthia. 



The styles are rudimentary in a much greater degree than 

 the cerci, although not such old structures. They occur in 

 the same low grade of development elsewhere only in the 

 males of certain families of the Orthoptera, in Mantidas, and 

 many Locustida3, and are, as was first recognized by Wood 

 Mason J, perfectly homologous with the abdominal styles 

 which are seated upon the ninth ventral shield of many 

 Thysanura (Machilis, Lepisma, Lepismvna, Nicoletia), where 

 they assist in the forward movement of the body, and also 

 perform tactile functions ; in young Cockroaches also we see 

 them penetrated by strong nerves and muscles which gradually 

 become rudimentary. 



In opposition to these styliform appendages in their embry- 

 onic development are the gonapophyses, of which it need only 

 be said that they make their appearance in the female only 

 at the retractation of the eighth and ninth ventral plates in 

 the form of processes in the neighbourhood of the sexual 



* " Nouveau Systems des Blattaires," in Verh. zool.-bot. Ges. in 

 Wien, 1865, p. 15. 

 t Arb. Russ. Entoin. Ges. 1879. 

 | Trans. Ent. Soc. Lond. 1879, p. 181. 



