Anatomy o/Daphnia. 251 



on the anterior edge, and collecting near the posterior inferior 

 part into one large trunk, which runs along the back of the 

 shell, and returns to the arterial heart again. The legs are 

 five pairs, all differing in many respects from each other, and 

 serving a different purpose than as organs of locomotion. 

 The first pair (plate ix. fig. 5.) are the smallest and most 

 simple of construction, and are situated immediately behind 

 the mouth, being inserted into the body of the insect by the 

 first joint (a), which is long and nearly cylindrical. It has 

 four joints ; the second being in form of a large vesicle (b) ; 

 the third joint is fixed to the inferior part of the vesicle (c), is 

 nearly triangular, compressed, and furnished at the inferior 

 edge with ten long needles (d), situated all on the same plane, 

 like the teeth of a comb. Attached to one corner of this 

 third joint is an appendix (e), small, and terminated by a 

 small spine, accompanied with a needle similar to those of the 

 preceding joint ; this is called a fourth joint by Straus. The 

 second pair (fig. 6.) are larger than the first, and are articu- 

 lated to the body a little behind them ; the second joint (b) 

 or vesicle is more heart-shaped than in the first pair, and the 

 third joint (c) is much flatter. It is a slender plate, quadri- 

 lateral, attached by its upper edge to the preceding joint, and 

 carrying inferiorly five strong plumose needles (d). The ap- 

 pendix to the third joint (e) is larger than the corresponding 

 one in the first pair, and is terminated by two long spines. 

 On the anterior edge of the third joint we see attached to it 

 a slender, semicircular-shaped branchial plate (/), which has 

 on its free unattached edge a row of twenty needles, ar- 

 ranged like the teeth of a comb, the last of which is the long- 

 est. In the third pair (fig. 70> the first and second joints 

 (a & b) are much the same, but larger than those of the prece- 

 ding pair. The branchial plate (c) is attached to the external 

 face of the second joint ; is larger and longer than in the prece- 

 ding pair, having seventy-six filaments on its free edge ; and 

 has at its posterior extremity a small ovular appendix of the 

 same nature as the branchia, and terminated by four bran- 

 chial filaments. The third joint (d) is attached to the inter- 

 nal edge of the second; it is a large, almost square plate, 

 and sends forth from its posterior border four flat, plumose 



