EXTERNAL CHARACTERS 157 



c. The cerci are a pair of many -jointed styles, attached 



under the lateral edges of the tenth tergum and 

 projecting backwards. 



d. The sterna on the ventral surface resemble the terga 



on the dorsal surface. The first is rudimentary. 



In the male the ninth sternum bears a pair 

 of styles. 



In the female the seventh sternum is pro- 

 duced backwards into a large boat-shaped process, 

 which forms the lower wall of the large genital 

 pouch. The hinder sterna are modified in relation 

 with the sexual apparatus, and are completely 

 hidden by the seventh. 



B. The External Apertures. 



1. The mouth opens on the ventral surface of the head, 



behind the labrum and between the jaws. 



2. The anus is at the hinder end of the body, beneath the 



tenth abdominal tergum and between the podical 

 plates. 



3. The genital aperture is single, and is placed at the 



hinder end of the body, ventral to the anus. It is 

 larger in the female than in the male, and will be 

 better seen at a later stage of the dissection. 



4. The stigmata, or spiracles, are the respiratory apertures, 



twenty in number. There are two large thoracic 

 ones on each side, one between the prothorax and 

 the mesothorax, and the other between the meso- 

 thorax and the metathorax. A pair of abdominal 

 stigmata are situated between the lateral margins 

 of the tergum and the sternum of each of the first 

 eight abdominal segments. 

 0. The Appendages. 

 1. The head appendages are four pairs. 



a. The antennae are very long slender many -jointed 

 and freely movable filaments, which arise from a 

 pair of oval arthrodial membranes just in front of 

 and below the eyes. 



