12 



and exopodites also two-jointed, Init no trace of endopo- 

 dites. The external angles of the joints are furnished 

 with short spines. The fifth pair are rudimentary, are 

 attached to the posterior end of the genital segment, and 

 consist of a thin lamella, furnished with three setae along 

 the posterior margin. Situated on the middle line 

 between the second maxillipedes is a strong chitinous 

 plate with a bifid apex pointing posteriorly. This is 

 known as the sternal fork, Init its function is unknown.* 



The external openings are the mouth, the vulvae, the 

 openings of the oviducts and vasa deferentia and the anus. 

 The mouth (Plate II., fig. 1 and fig. 8) is situated on the 

 ventral surface of the cephalo-thorax, and is placed at the 

 apex of a short, movable, conical tube. This tube is com- 

 posed of the upper and lower lips fused toijether. The 

 vulvae (Plate II., fig. 6) are situated on each side of the 

 middle line near the posterior end of the genital segment, 

 and communicate with the " receptacula seminis.'' They 

 are difficult to see in the adult female, but have each 

 frequently a spermatophore attached which indicates the 

 position. The openings of the oviducts are in the same 

 segment, but nearer the lateral margins and just under 

 the fifth feet. The openings of the vasa deferentia (Plate 

 II., fig. 5) ai'e situated on the postero-lateral margins of 

 the genital segment of the male. The anus is situated in 

 the middle line at the apex of the abdomen. In 

 addition to these more important openings, there are also 

 apertures of pore-canals and glands on the anterior 

 surface of the basal joint of the protopodites of the second 

 and third pairs of feet, and also on the dorsal surface of 

 cephalo-thorax and abdomen. The opening in some cases 



• Mr. I. C. Thompson suggests that the sternal fork appears to him to 

 be a support or crvitch, serving to raise the body sufficiently from the host 

 to enable cither the s\^^mming feet or the moiith organs to be used, but 

 I have not seen it used in this manner, 



