1920] Du Porte: Muscular System of Gryllus 41 



PLEURAL MUSCLES. 



(a) Noto-pleural. 



99. The Fourth Lateral Muscle. Homologue of 87, q. v. [9]. 



100. The Fifth Lateral. Homologue of 88, q. v. [10]. 



(b) Sterno-pleural. 



The sternopleural milscles (101 to 105) all originate from the 

 lateral border of the sternite in succession from the anterior to 

 the posterior end of the sclerite. They are inserted into the 

 pleural sclerites or into the spiracle, as follows: 



101. The First Lateral, into the first pleural sclerite. [6]. 



102. The Second Lateral, into the third pleural sclerite. [7]. 



103. The Dilator of the Spiracle, into the process of the bow 

 •of the spiracle. [11]. 



104. The Third Lateral, into the second pleural sclerite. [8]. 



105. The Third (a) Lateral, with 104 into the second pleural 

 •sclerite. 



Functions of the Foregoing Abdominal Muscles. The longi- 

 tudinal muscles are retractors of the abdomen. The ventral 

 and dorsal working together telescope the segments. The 

 ventral bend the body downwards, while the dorsal act as their 

 antagonist muscles, bending the body upwards. The tergo- 

 sternals and laterals are expiratory muscles, and pull the sternum 

 and tergum together. Those of either side working alone may 

 .act as rotators of the abdomen. 



THE EXTREMITY OF THE ABDOMEN. 



In both sexes ten dorsal segments, including the suranal 

 plate (Figs. 3, 33, 35, P. S.) can be readily distinguished. On 

 the ventral side, however, there are only eight in the female and 

 nine in the male, including the subgenital plate. A study of the 

 musculature as described below will show, apart from other 

 evidence, that in the female the supra-genital plate, lying above 

 the ovipositor is the sternite of the ninth segment, and in both 

 sexes the podical plates (P. P.) are the divided halves of the 

 tenth sternite. 



