Chap. XIII.] THE COCKROACH. 



mid-line. Their basal moieties are broad, and serve to 

 of the roof of the genital pouch. At the base of their 

 moieties a chitinous slip passes to the eighth and ninth terga. 

 The posterior gonapophyses (pos. gon.), which normally lie above 

 the anterior pair, are divided into two portions, the inner slender 

 and hard, the outer larger and soft. In the cockroach these 

 appendages grasp the egg-capsule while it is being extruded 

 from the genital pouch. The notched dorsal edge of the capsule 

 bears the imprint of the inner portion of the posterior gon- 

 apophyses. In some insects this apparatus is curiously modified 

 to form an ovipositor, by means of which holes are bored in 

 earth, wood, or animal tissue, for the reception of the ova. In 

 the bee the sting is a specialised form of the same apparatus. 



Two cigar-shaped sixteen- jointed processes, the cerci, which 

 probably have a sensory function, spring in both sexes from the 

 edges of the tenth somite. On either side of, and slightly 

 dorsal to, the vent, there are, in both sexes, triangular podical 

 plates, regarded by some anatomists as the terga of an eleventh 

 abdominal somite. 



Ten terga and nine sterna can be made out in the male ; but 

 the first sternum is, as in the female, rudimentary. Attached 

 to the ninth sternum are two slender sub-anal styles. There is 

 also a complex system of plates and hooks, concealed within 

 the ninth sternum, and constituting the male genital armature. 



If we take the podical plates to represent an eleventh ab- 

 dominal segment, the number of segments in the cockroach 

 would seem to be seventeen, three cephalic, three thoracic, and 

 eleven abdominal. 



The apertures of the body are as follows : 



1. The mouth, lying between the labrum and the labium, and 

 bounded laterally by the mandibles and maxillae. 



2. The vent, lying between the triangular podical plates. 



3. Twenty spiracles, ten on each side of the body, forming the 

 external orifices of the tracheal system. Eight on each side 

 are abdominal, between the sterna and terga ; two on each side 

 are thoracic, between the pro- and meso-, and the meso- and meta- 

 thorax. The thoracic stigmata are provided with external valves. 



