THE COCKROACH. 349 



The broad dijQferences in the structure of the abdomen of 

 the male and female have been already pointed out. Of the 

 eight terga externally visible in the female (Fig. 98), the first 

 is shorter than those which succeed it ; and the hindermost 

 (Fig. 98, 10) is escutcheon-shaped, deflexed at the sides, thin 

 in the middle, and notched at the end. When this tergum is 

 gently pulled backward, two other very narrow terga (Fig. 

 98, 8, 9), of which the anterior overlaps the posterior, and 

 which were hidden between it and the antepenultimate or 

 seventh tergum, become visible. The apparent eighth tergum 

 is therefore really the tenth. Beneath the tenth tergum are 

 two triangular j90C?ica^ plates (Fig. 98, 11), one on each side 

 of the anus. Provisionally, I take them to be the scleriies of 

 the eleventh abdominal somite. 



The first sternum is confluent with the second, and largely 

 hidden by the coxce of the metathoracic limbs. The seventh 

 is greatly enlarged, and its posterior edge is produced into a 

 boat-shaped process, nearly divided into two portions by an 

 inward fold of the integument along the median line. 



Completely hidden by the seventh sternum is a thin plate, 

 narrower in front than behind, where it is produced on each 

 side. Anteriorly, it is articulated with the sternum of the 

 following somite, so as to form a sort of spring-joint, which 

 ordinarily keeps it applied against the latter, and therefore 

 directed obliquely upward and a little forward. The large 

 aperture of the vulva (Fig. 98, v) lies in the middle of this 

 plate. On the sternal region behind the vulva, between it 

 and the anus, arises a pair of elongated processes, divided 

 into two portions, of which the outer is thick and soft, the 

 inner slender, pointed, and hard. They embrace and partly 

 ensheath two other processes, having somewhat the shape of 

 knife-blades, the anterior fixed ends of which are curved, and, 

 being attached to the sides of the somite to which they be- 

 long, are distant, while the blades meet, and are applied to- 

 gether in the middle line. Of these, which may be termed 

 gonapophyses^ the study of their development shows that the 

 posterior bifid pair belong to the ninth somite, while the an- 

 terior pair belong to the eighth. 



The cerci (x) are attached to the dorso-lateral part of the 

 tenth somite. 



In the abdomen of the male Blatta (Fig. 99) the ten terga 

 are readily discernible ; but the eighth and ninth are very 

 short, and the former overlaps the latter. The tenth tergum 

 is flat, and has a freely-projecting, truncated, posterior mar- 



