STATE GEOLOGIST. 165 



•covered with hairs. The fourth joint is more slender than the 

 preceding, and terminates in a process below, which bears besides a 

 long hair a peculiar blunt bristle, that serves some unknown 

 purpose — probably being sensory in function like the similar hairs 

 on the antennae of some Cladocerae. 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 are coalescent, followed 

 by a hinge joint and two elongated segments. 



The second antennae 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 

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

 The last segment of the abdomen bears two stylets, which are some- 

 times considered as together constituting an additional segment. 

 Each of these stylets has, with several small spines, two elongated 

 ■caudal setae, one of which is usually as long or longer than the 

 entire abdomen. 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 caeca or blind sacs, as in 

 some other Copepoda. The canal is divided into four more or less 

 distinct portions; the first section is a slender, muscular tube, ex- 

 tending from the mandibles nearly through the first segment, 

 opening into the stomach proper, which is a muscular and gland- 

 ular sac or tube, filling the greater part of the thorax ; at the be- 

 ginning of the abdomen, the sac is constricted and becomes the in- 

 testine proper ; near the extremity again there is another change 

 and the intestine loses its glandular character, and, by a peculiar 



