68 THE COCKROACH : 



branches, which open into the main longitudinal trunks. In 

 larvae with aquatic respiration these branches exist, though they 

 are not functional. 



Palmen's objections must be satisfactorily disposed of before 

 Gegenbaur's explanation, interesting as it is, can be fully 

 accepted. Palmen has proved, what is on other grounds clear 

 enough, that stigmata are more ancient than trachea! gills, 

 aerial tracheate respiration than aquatic. But there is nothing 

 as yet to contradict the view that the first Insect-wings were 

 adapted for propulsion in water, and that they were respiratory 

 organs before they became motor. It is Gegenbaur's explana- 

 tion of the origin of stigmata, and not his explanation of the 

 origin of wings, which is refuted by Palmen. 



Abdomen. 



In the abdomen of the female Cockroach eight terga (1-7 ; 

 10) are externally visible. Two more (8, 9) are readily dis- 

 played by extending the abdomen ; they are ordinarily 

 concealed beneath the seventh tergum. The tenth tergum is 

 notched in the middle of its posterior margin. A pair of 

 triangular " podical plates," which lie on either side of the 

 anus, and towards the dorsal surface, have been provisionally 

 regarded by Prof. Huxley as the terga of an eleventh segment. 

 Seven abdominal sterna (1-7) are externally visible. The first 

 is quite rudimentary, and consists of a transversely oval plate ; 

 the second is irregular and imperfectly chitinised in front ; the 

 seventh is large, and its hinder part, which is boat- shaped, is 

 divided into lateral halves, for facilitating the discharge of the 

 large egg-capsule. 



In the male Cockroach ten abdominal terga are visible 

 without dissection (fig. 33, p. 70), though the eighth and 

 ninth are greatly overlapped by the seventh. The tenth 

 tergum is hardly notched. Nine abdominal sterna are readily 

 made out, the first being rudimentary, as in the female. The 

 eighth is narrower than the seventh, the ninth still narrower, 

 and largely concealed by the eighth ; its covered anterior part 

 is thin and transparent, the exposed part denser. This forms 

 the extreme end of the body, except that the small sub-anal styles 

 project beyond it. The podical plates resemble those of the 

 female. 



