56 Illinois State Laboratory of Natural History. 



crease rapidly in length at the i)osterior end and fade away 

 in front. The male does not have this character, and adult 

 females are very rarely found without it. Of the four apical 

 In-istles the middle two are well developed. The inner one 

 of this pair is much longer than the outer. The innermost 

 of the four is a very slender seta. The outermost varies in 

 character from a long seta hordered externally hy harhules 

 and internally by long slender cilia, to a long strong spine 

 serrate on both sides. It may be anywhere from one half 

 to four fifths as long as the stylet. 



The first antenna3 are twelve-segmented. Dr. Schmeil 

 notes the presence of a minute sensory bristle on the ninth 

 segment in the place occupied by the sense-club on the 

 twelfth segment of seventeen- segmented antenna-. It is 

 very inconspicuous indeed. The last three segments are 

 usually very long and are armed on the inner side by hyaline 

 plates. 



The usual armature of the swimming feet is as follows : — 

 First pair : outer ramus, three spines, five setae ; inner 

 ramus, one seta, one spine, four sette. Second and third 

 pairs : outer ramus, four spines, live setcT ; inner ramus, 

 two spines, four setie. Fourth pair : outer ramus, three 

 spines, live setue ; inner ramus, one seta, two spines, two 

 sets'. 



The fifth foot (PI. XYIII., Fig. 2) is one-segmented and 

 plate-like. On the inner side is a very strong serrate spine. 

 At the tip, borne on a cone-shaped projection, is a very long 

 slender seta, parallel to the spine. On the outer side is a 

 delicate little seta projecting outward at a considerable angle. 



The rcfcjifdciihiin .-tciiiinis (PL XYIII., Fig. 3) is almost com- 

 pletely divided iuto an anterior and a posterior part, by a 

 median constriction. The i)orus is situated in the middle of 

 this narrow connecting part. The lower half extends down 

 into the narrow part of the first abdominal segment. The 

 spermal canals are attached to the receptaculum at the outer 

 angles of the lower part. 



The egg- sacs are usually long, with many eggs, but some- 

 times contain only a few, arranged in a spherical mass. 



