Constitution of the Body in the Blattidse. 233 



aperture. The anterior pair of gonapophyses remains simple 

 and originates on the eighth segment, while the posterior 

 pair forks secondarily and springs from the ninth segment ; 

 the position of these gonapophyses therefore corresponds to 

 that ascertained for the above-mentioned Thysanura, as well 

 as the position of the parts of the ovipositor in Grasshoppers 

 and Aculeate Hymenoptera, so that these appendages may 

 probably be regarded as homologous structures. 



On the other hand the paired uncinate hooks of the male 

 of Phyllodromia appear to originate on the tenth ventral 

 plate, so they should not be regarded as homologous with 

 the developed valves of the penis in MachiUs, which are 

 seated upon the ninth abdominal ring, but, like the numerous 

 other chitinous pieces around the male genital aperture, only 

 as partial thickenings of the wall. These chitinous projec- 

 tions probably all serve to open and dilate the vagina of the 

 female, especially as a perforated penis, which is highly 

 developed in Machilis, seems to be wanting in the Blattidse. 



As Cholodkovsky proved, leg-rudiments perfectly homo- 

 logous with the thoracic legs are formed in the young embryo 

 from the first to the ninth abdominal segment. Of these 

 embryonic appendages the first pair then become converted 

 into peculiar branchiiform organs (/. c. p. 94), which disappear 

 before the exclusion of the embryo ; in fact on the first 

 abdominal segment even of older embryos we find only the 

 median ventral shield, which is surrounded by soft, trans- 

 versely folded connective membrane. On the second to the 

 ninth segments of the same stage the leg-rudiments undergo 

 a plate-like change of form. 



On the nearly mature embryo of Phyllodromia I find on 

 the isolated ventral surface of the first abdominal segment 

 only the median ventral shield representing the sternal plates 

 of the thorax. On the second segment a median shield 

 which is pretty strongly chitinized at the hinder margin also 

 occurs in the middle, but on each side there is a plate more 

 strongly chitinized, especially towards the lateral margin, but 

 which is also covered with fine wavy wrinkles and short 

 spines. The median ventral shield which is situated above 

 the lateral plates is separated from the latter by delicate 

 longitudinal folds, which may be traced distinctly as far as 

 the seventh abdominal segment. 



On the adult animal the tripartition of the ventral plate is 

 distinctly retained only on the second abdominal segment, 

 while the other ventral plates form a single shield on which 

 no trace of longitudinal folds can any longer be recognized. 

 Indications of this constitution of the ventral plates are still 



Ann. & Mag. N. Hist. Ser. 6. Vol. v. 18 



