14 THOMAS SAY FOUNDATION 



the penis, lying in the middle line in front of the for- 

 ceps and between the claspers. It is the most complex 

 organ of all, and is of prime importance. A complete 

 homology of its various forms would occupy a volmne 

 and require years of study. It is usually two- jointed, 

 the basal joint being a simple support. The distal 

 segment is in most cases fairly well chitinized, and is 

 essentially a swollen tube bearing various flat plates 

 and slender processes, a further account of which will 

 be found in the specific descriptions. 



The two segments of the hypopygium are deeply 

 grooved beneath to receive these organs when they are 

 in repose. The penis and claspers are supported on 

 a firm mass of tissue which is attached on each side 

 well forward, at the front lower corner of the second 

 segment. This enables the penis and claspers to move 

 up and down, as a consequence of which they seem 

 sometimes to be longer in comparison with the for- 

 ceps than they seem at other times, or in other speci- 

 mens, — a point to be remembered in comparing speci- 

 mens with each other or with figures. The penis 

 bends forward and back freely, and is figured either 

 way. 



On the ventral side of the abdomen, anterior to 

 the genitalia, is another structure of importance, the 

 fifth abdominal sternite. It will be apparent on in- 

 spection that there is at the base of the abdomen a 

 short sternite before the one that matches the first 

 visible tergite (indicating that the apparent first ter- 

 gite is a combination of the first and second) ; count- 

 ing from this basal sternite, the fifth lies partly con- 

 cealed within the ends of the (apparent) fourth ter- 

 gite. It is deeply forked behind in the shape of a V 

 or U, and often shows characters of specific import- 

 ance, either brushes of very short spines, or blunt pro- 

 cesses, sinuosities of outline, etc. 



