ORTHOPTEROIDEA iPANORTHOPTERA) 235 



stage each leg consists of five segments: a basal piece (representing sub- 

 coxa, coxa, and trochanter) the femur, the tibia, the tarsus, and a terminal 

 segment. By the 120-hour stage the basal segment divides into two 

 segments, the proximal one representing the subcoxa, the tarsus becoming 

 three-segmented. During blastokinesis the trochanter is differentiated. 



A pair of appendages is formed on each of the 11 abdominal segments. 

 Those on the first are the pleuropodia. Appendages of segments two 

 to seven are small and disappear during blastokinesis. The eighth pair 

 is also small and in the male disappears completely. The ninth pair 

 persists in the female as an ovipositor valve; the tenth pair in the same 

 sex disappears during blastokinesis. In the male the ninth and tenth 

 pairs fuse to form the aedeagus and associated parts. The appendages 

 of the eleventh segment form the cerci in both sexes. 



The pleuropodia arise in the 53-hour stage as lateral evaginations in 

 the same way as the thoracic appendages with which they are homologous. 

 They attain a maximum development during blastokinesis when they are 

 about 0.35 mm. long (Fig. 161). After blastokinesis they shrivel up, 

 to be cast off at time of hatching. 



A typical segment of the body divides into a median sternum and two 

 lateral primary tergites. The sternum is divisible into a median part 

 and two lateral parts which bear the appendages. This applies from the 

 mandibular to the tenth abdominal segments. In the thorax the legs 

 move laterally and come to lie at the junction of the tergum with the 

 sternum, the subcoxal segment growing to form a large sclerite, the 

 pleuron, between the tergum and the sternum. The pleuron later divides 

 into an anterior episternum and a posterior epimeron. 



The number of segments composing the head of Locusta migratoria is 

 seven, as supported by the evidence from the coelomic cavities, the 

 appendages, and the neuromeres. Furthermore, according to Roonwal, 

 although the evidence points to the existence of a labral segment in 

 insects, it is difficult to fit in with the general scheme of the arthropod 

 head. 



Regarding the segmentation of the abdomen in Locusta, it has been 

 shown that 11 segments take part in its formation. The eleventh, like 

 those which precede it, is provided with a pair of appendages, a pair of 

 coelomic cavities, and a neuromere. The telson is not distinct in Locusta. 

 Thus exclusive of the acron and the telson there are 21 segments in all. 



When the embryo is about 59 hours old, a thin membranous provi- 

 sional dorsal closure is formed (Fig. 154, dc). It arises from the lateral 

 edges of the embryo at a point slightly above the origin of the amnion 

 and covers the entire dorsum, cutting off the yolk from contact with the 

 inner side of the embryo. Its method of formation has not been deter- 

 mined in Locusta. Graber (1888) states that in Stenohothrus variabilis 



