126 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



bristle that serves some unknown purpose — probably being sensor jr 

 in fnnctiou like the similar hairs on the antennae of some Gladocerce^ 

 The next joint is shorter than the rest, while the remaining three are 

 spined at definite points. The antennae of the male are curiously- 

 altered, or geniculate, on both sides, as in Cyclops. The three basal 

 joints are shortened, while more or fewer of the following ones ar& 

 coalescent, followed by a hinge joint and two elongated segments. 



The second antenna) or antennules are two-jointed, and the basal 

 joint has a two-jointed branch or palp; the terminal joint is covered 

 with spines; at the end are longer and curved spines, jointed in the 

 middle. 



The mandible is a flattened plate with digitate teeth at the end, on 

 one side of which springs a two jointed palp, and from the other a 

 blunt process. The maxilla is somewhat like it, but has rudiments 

 of other elements. 



The first pair of feet have two three-jointed rami. The outer 

 ramus is shorter and with the longer branch is directed forward. 

 The fourth foot has the inner branch two-jointed. The inner branch 

 of the third foot of the male is peculiarly modified to form a pre- 

 hensile organ, as it is this foot which fastens the spermatophore to 

 the female. The fifth feet are composed of two flat plates. 



The second division of the body, the abdomen, consists of five seg- 

 ments, of which, however, the first two are united in the female. The 

 last segment of the abdomen bears two stylets, which are sometimes 

 considered as together constituting an additional segment. Each of 

 these stylets has, with several small spines, two elongated caudal 

 setse, one of which is usually as long or longer than the entire abdo- 

 men. The stylets are usually considerably longer than wide, but the 

 proportions vary somewhat in different species. 



Viscera: The body cavity is traversed by the alimentary canal^ 

 which is a straight tube with no lateral cceca or blind sacs, as in some 

 other Cojiejwda. The canal is divided into four more or less distinct 

 portions; the first section is a slender, muscular tube, extending from 

 the mandibles nearly through the first segment, opening into the 

 stomach proper, which is a muscular and glandular sac or tube, filling 

 the greater part of the thorax; at the beginning of the abdomen, the 

 sac is constricted and becomes the intestine proper; near the extrem- 

 ity again there is another change and the intestine loses its glandular 

 character, and, by a peculiar adaptation becomes a sort of force-pump, 

 which, during life, is constantly pumping water in and out, serving 

 as a means of respiration. This anal respiration is quite common 

 among aquatic animals in this as well as other orders. This latter 

 section of the canal is the rectum, and opens beneath a toothed anal 



