ECONOMY OF THE DAPHNIA. 163 



of the valves, but occasionally it will be lifted by means of a long 

 muscle (;;/, Fig. ii), inserted in its front wall, and arising from the 

 back of the head, between the coeca or rudimentary liver, which will 

 be hereafter described. A large nervous ganglion (§', Fig. ii) 

 occupies a considerable portion of its cavity, and blood corpuscles 

 circulate freely within it. Probably it is the seat of the sense of 

 taste. The labrum is much more conspicuous in the embryo 

 young (Fig. 1 7) than in the adult. 



The remaining limbs attached to the thoracic region of the 

 body, together with the abdomen, are included within the valves 

 of the carapace, and are more difficult of observation. An 

 oscillating movement just below the anterior margin of the 

 valves indicates the position of the mandibles {m d, Figs, i, 3, 4, 

 and 11). These are stout, bent pieces. If carefully traced, they 

 will be seen to play on a pivot at the junction of the head with 

 the carapace, and it will be noticed that their free extremities 

 work against each other with a motion somewhat like that of the 

 gizzard of the Pitcher Rotifer, but this can only be clearly seen 

 when the observer is fortunate enough to get a front view of the 

 animal between the valves. Below the mandibles are a pair of 

 maxillae described by Baird, but I have not succeeded in seeing them. 



Following these are the five pairs of feet (i, 2, 3, 4, 5, 

 Fig. 4) ; Baird has described them in detail as found in Daphnia 

 Schcefferi, enumerating the several joints of which they are 

 composed, together with the setse, etc., appended to them; I 

 must, however, content myself with general observations. The 

 first pair of feet are modified in the male (Fig. i). They are 

 furnished with a claw and a long filament, which floats outside the 

 shell, and supplies a very good sexual character. The males may 

 at once be distinguished by this filament together with the greater 

 size of the superior maxillae (Fig. i). In all these limbs it 

 appears to me that two parts may be distinguished ; an external 

 pouch-like organ (Fig. 4) and an internal part curiously modified 

 and furnished with plumose setae and combs (Figs, i, 2, and 19). 

 Probably we have here again the exopodite and endopodite. The 

 pouch-like organs can be easily seen through the valves of the 

 carapace ; they are furnished with a soft integument lined by 



