Tate : The Organization of " Daphnia Pulex." 131 



and the stomach do not go on together, nor do the two caeca act at 

 one time. When one is active the other is passive, and for the most 

 part both are quiescent. This curious pair of blind sacs reminds us 

 of the similarly located coronet of ca3ca in Orthoptera and lieiniptero^ 

 usually regarded as analagous to the liver of higher animals ; but the 

 fact that the former afford lodgment for particles of food while the 

 latter never do, forbids any further inference. Still less are they to be 

 interpreted as the homologues of the two caeca in Brachyura, or the 

 single caecum in Macrura^ the rudiment of the yelk-sac of the embryo, 

 these being connected with the opposite end of the stomach. That 

 they are lateral diverticula of the stomach, and its functional allies, is 

 clear. The adaptation for food already partly assimilated (animal) 

 which the straight course of the digestive track indicates (while a 

 vegetable diet is more or less constant) must not be lost sight of in 

 any attempt to decipher these unique organs. The homologues of the 

 hepatic organs of higher Crustacea must be sought for, not in these 

 but in the similarly situated glandular masses overlying the pyloric 

 extremity of the stomach. The stomach itself is of uniform diameter 

 throughout, and extends in a straight course backwards, as far as the 

 fifth or sixth segment, when it gives place to the rectum. The latter 

 is continuous with the stomach, but bends downwards, its termination 

 being closed by a powerful muscular sphincter. Beyond this is a 

 cloacal cavity ending in an anus between two toothed arches on the 

 dorsal aspect of the telson. This caudal plate is triangular, flat- 

 tened, and tipped with two powerful horny hooks, with which the 

 animal cleanses and guards the entrance into the shell. The seventh, 

 or preceding segment, is also armed with a pair of long stiff bristles ; 

 these defensive weapons being vigorously used on the approach of * 

 any danger from behind. Nimierous globular vesicles underly the 

 abdominal region near the rectum. Judging from the renal organs 

 in Gammai iis pulex and some ' iher crustaceans, we m.ay conclude that 

 they serve the same function as the kidneys in higher animals. 



The carapace consists of two horny flexible oval pieces, soldered 

 together along the dorsal line, but capable of a considerable deg^-ee of 

 expansion along their ventral edges, whence the tail and most of the 

 body can be protruded at jh'j'-nre. The cephalic portion o^ the 

 carapace, as far back as the a: ' °s anherent to the body. Seen from 

 above, it is heart shaped, thf . x forming the apex. Where the free 

 edges of the two valves consti>.u.dng the remaining body carapace meet 

 posteriorly, is produced, from tne two valves, but in one piece, a long 



