78 Proceedings of the Royal Physical Society. 



At once the fleas began to quicken their sluggish scramblings, jumping up 

 and down and tumbling over one another. Two $ $ were selected for 

 closer observation. Soon one was seen to jerk his posterior segments 

 upwards repeatedly. Watching him with an aplanatic lens ( x 20) I could 

 see that the 8th tergites 1 were plainly diverging while the "fingers" of 

 the clasper were in motion up and down. 2 Suddenly he ran to a $ , 

 shoved his head below her till his frons rested beneath and slightly behind 

 her posterior coxa?. At the same time his forelegs seemed to catch 

 momentarily the hind ones of the $ , pinning her down and forcing her to 

 elevate the posterior segments, which were at once gripped by the upturned, 

 outspread 8th tergites of the $ . Thus in coitil the last sternites of the 

 $ are opposed to the last tergites of the $ and vice versa. The coupled 

 pair usually remain at rest but they may crawl about freely, all twelve 

 legs (which, owing to the position adopted, fall in the same plane) being- 

 used for locomotion. Copulation often took place in the neck of the 

 bag in which the nests were kept, but, once paired, the insects showed 

 a tendency to hide themselves in the debris at the bottom. 



The position of the sternites and tergites concerned is, in farreni, briefly 

 as follows : — 



The 8 th tergite $ covers a large portion of the end of the £ abdomen. It 

 reaches back as far as the apex of the 7th sternite (which it fully covers) 

 lying well over the sinus. It even touches, and may possibly sometimes cover, 

 the posterior ventral angle of the 7th tergite. Below it also lie the $ 

 sternites 8-10, and part of tergite 8, viz., the distal ventral region which 

 is bristly on both sides. The 8th sternite $ rests so that the long terminal 

 bristles lie on the pygidium of the % . A slight general movement out- 

 wards of the 9th tergite $ has taken place so that the " finger " is above 

 the sinus of the 7th sternite $ . Proximally and ventrally the 9th sternite 

 $ is pressed up against the 10th sternite $ . At the point of contact 

 their respective bristles and spines interlock, while the " stylets " are held 

 in the V-shaped collar formed by the almost terminal lateral flaps of the 

 8th tergite $ . The distal hairy portion of the 9th sternite $ is pushed 

 well forward, its apex appearing below the 7th tergite $ , in which position 

 it seems not only to hold the $ but also to act as a support for the 

 extended chitinised portion of the penis. The rcc&ptacxdum seminis 

 is backwardly displaced and its sinuous duct partially straightened in 

 copulation. The thin, free, distal portion of the penis, which ordinarily 

 lies coiled like a watch-spring between two chitinous, triangular, basally- 



1 Strictly speaking the halves or lateral lobes of the 8th tergite. 



2 Probably to unlock the hairs, etc., of their inner surfaces. 



