DAPHNIA. 



[ 236 ] 



DASYA, 



D. Wingii (PI. 20. fig. 27). Fresh- 

 water. 



BIBL. Baird, Brit. Entomos. 109. 



DAPH'NIA, Mull. A genus of Ento- 

 mostraca, of the order Cladocera, and family 

 Daphniadae. 



Char. Head produced into a more or less 

 prominent beak ; superior antennae situated 

 beneath the beak, either one-jointed or con- 

 sisting of a minute tubercle with a tuft of 

 short filaments ; inferior antennae large and 

 powerful, two-branched; one branch three- 

 jointed, the other four-jointed; five pairs 

 of legs. 



Valves of the carapace finely reticulated, 

 and terminated below by a longer or shorter 

 serrated spine. Anterior branch of inferior 

 antennae (PI. 20. fig. 286) four-jointed, first 

 joint very short; from the end of the third 

 a long filament arises ; and the fourth joint 

 is terminated by three others ; posterior 

 branch three-jointed, the first and second 

 joints sending off a long filament, the third 

 terminated by three of them ; the filaments 

 are jointed near the middle, and usually 

 feathery. Eye spherical, with about twenty 

 lenses. Labrum (PI. 20. fig. 35) flattened, 

 and with a large hairy lobule at the end. 

 Mandibles (PI. 20. fig. 34) consisting of a 

 fleshy -looking body, bent inwards near the 

 end, and terminated by numerous minute 

 teeth. Jaws (PI. 20. fig. 36) composed of a 

 strong body terminated by four horny spines, 

 three of which are curved inwards. Legs five 

 pairs, those of the first pair in the female 

 (PI. 20. fig. 29) three-jointed; upon the 

 outer edge of the second joint are three 

 small projections, each with four or five 

 long jointed setae; terminal joint very 

 small, and with one or two similar setae ; 

 the setae not plumose. In the male they 

 are more slender, with "a strong claw at the 

 end of the second joint, while the seta 

 arising from the terminal joint is very long, 

 nearly the length of the body, and" floats 

 outside the shell. 



The second (PI. 20. fig. 30), third (fig. 31), 

 and fourth (fig. 32) pairs of legs are bran- 

 chial and somewhat similar, the joint fur- 

 nished with jointed and mostly plumose 

 setae, and a branchial plate also giving off 

 numerous plumose setae. The fifth pair of 

 legs (fig. 33) are three-jointed, the portion 

 correspondingto the branchial plate rounded 

 and without filaments; above this is a 

 curved, jointed, and plumose spine, the 

 third and fourth joints forming finger-like 

 processes springing from the lower end of 



the leg, with two or three plumose setae. 

 The branchial legs are constantly in motion 

 during life; and this gives rise to the 

 quivering appearance seen in the Daphnue 

 with the naked eye or a simple lens. 



The ova on their escape from the body 

 become lodged between the back of the ani- 

 mal and the shell, where they remain until 

 completely hatched ; but at certain seasons 

 of the year ephippial or winter ova (PI. 20. 

 fig. 37) are produced (ENTOMOSTBACA). 



According to Lubbock's observations, the 

 latter only are true ova ; although both 

 kinds become hatched and perfectly deve- 

 loped, this may occur without impreg- 

 nation. 



Seven British species of Daphnia are re- 

 cognized : some of them may be found in 

 almost every collection of water, which they 

 frequently colour. 



D.pulex (PI. 20. fig. 28) (common water- 

 flea). Valves oval, their dorsal margin not 

 serrated ; head large, rounded above and in 

 front ; superior antennae (PL 20. tig. 28 a) 

 very small; filaments of inferior antennae 

 plumose ; posterior portion of abdomen with 

 four projections at its curve, the first pro- 

 longed and bent upwards ; below these are 

 two jointed filaments ; the end portion has 

 two dentate arches, and 

 terminates in two strong 

 hooks. 



Some other species are 

 common ; but their essen- 

 tial characters have not 

 been briefly expressed. 



BIBL. Baird, Br. En- 

 torn. 89; Lubbock, Ann. 

 N. H. 1857, xx. 257; 

 Leydig, Daphnid. 1860; 

 Weismann, Daphniden, 

 1877, and Zeitschr. wiss. 

 Zool. 1876, 7. 



DARWINEL'LA, 

 Brady, ( = PolycMes, B.). 

 A genus of Ostracode 

 Entomostraca. 



1 British species: D. 

 Stevewoni. 



BIBL. Brady, Ann. 

 N. H. ser. 4. vi. 25. 



DA'SYA, Ag. A ge- 

 nus of Rhodomelaceae Dasya KUtzingiana, 



(Florideous Algae), con- with a stichidium 



. ,. e , f , P ni and two rows of 



sistmg of tufted hlamen- tetraspores. 

 tous sea- weeds, of a red, Magnified so dia- 

 brown, or purple colour, 

 growing on rocks near low- water mark. 



Fig. 157. 



