126 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
bristle that serves some unknown purpose— probably being sensory 
in function like the similar hairs on the antennz of some Cladocere. 
The next joint is shorter than the rest, while the remaining three are 
spined at definite points. The antenne 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 are 
coalescent, followed by a hinge joint and two elongated segments. 
The second antenn 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 
setee, 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 ceca or blind saes, as in some 
other Copepoda. 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 bécomes a sort of forece-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 
