102 ANATOMY OF AN ARTHROPOD. 



epicranium comes the cJijpeus (fig. 39 a, c), a broad plate, 

 which is followed by a smaller plate united to the front of 

 the clypeus, called the lahnivi or "upper lip" (L). The plate 

 on each side below and behind the eyes is called the gena or 

 cheek (Gr). Ocelli are absent in this type, otherwise they would 

 be situated on the epicranium. The tJiorcw is composed of 

 three segments, united by sutures. Each segment is known 

 respectively as the pro-, meso-, and metathorax (fig. 38, Th). 

 Each ring is composed of an upper plate, the notum or tergum, 

 and a lower plate, the sternum, so that in the thorax we have 

 pronotum, meso-, and metanotum above, and the pro-, meso-, 

 and metasterna below. The spaces between the nota- and 

 sterna are covered by chitinous plates, called the pleurae. The 

 }>ronotum, the upper portion, is prolonged over the neck. The 

 mesonotum, which is smaller than the pronotum, bears a pair 

 of leathery wings. These wing-covers are movably united to 

 the tergum or mesonotum. The metanotum also bears a pair 

 of thinner wings, the true organs of flight. If we are examining 

 Blatta orierdalk we shall not observe these in the female, nor 

 the second pair of wings. 



The abdomen (Ah) is flattened dorso-ventrally. It is com- 

 posed of ten distinct somites, the hinder ones being invisible, 

 as they are pushed into the anterior ones. The upper parts of 

 the segments are called terga (fig. 4:2, T). Of the ten, only 

 eight can normally be seen, the eighth and ninth being hidden 

 under the seventh. Situated at the side of the posterior ventral 

 anus are a pair of small plates called the poJical plates. It is 

 said that these represent an eleventh segment. They can easily 

 be observed by raising the tenth tergum. On the tenth tergum 

 are a pair of jointed processes called cerci (fig. 38, Ce). In the 

 male a pair of styles are also borne on the ninth sternum (•?). 

 The ntcnia are the ventral plates, the C(iuivalents of the tei'ga. 

 The seventh in the female bears a iirocess passing backwards, 

 forming part of the large genital pouch. 



Appendages of the head. — On the head are placed the antennas 



