STATE GEOLOGIST. 101 



The digestive system is the most conspicuous part of the creature when filled. 

 It is then often of a brillant green color, extending along the whole dorsal region. 

 The oesophagus is short, opening into the stomach just behind the brain gang- 

 lion. From this point the stomach curves upward and extends thence through 

 the whole length of the animal. The contractile vessicle above the stomach is 

 quite an obvious feature, but Gruithuisen sayh there are two hearts, one venous, 

 the other arterial, but this is probably not established, though the existence of a 

 dorsal vessel above the stomach is probable from analogy and observed appear- 

 ances. 



The legs, which are of five pairs, vary considerably, but the same plan is pre- 

 served. At the base of each is a branchial plate furnished with fine branchial 

 filaments corresponding to gills, while the remaining portions of the leg serve to 

 create currents of water toward the mouth. The result is a vigorous current 

 between the legs under the body, which transports the food particles to the max- 

 illae. The ovaries are along the sides of the abdomen, and the ova are normally 

 hatched within the shell of the parent above the abdomen. 



These creatures have been supposed hermaphroditic, from the extreme scarcity 

 of the males, but they are in this respect like the Aphides, being parthenogenetic. 

 Besides the ova which are hatched within the shell of the living parent, another 

 method is seen. The outside of the carapace grows opaque, and finally two spots 

 appear within which are the eggs. When the moult takes place, the carapace 

 with its burden is left in the water until a favorable time, when the eggs hatch. 

 This obviously is a protection against the cold of winter, for the ephippium, as 

 the carapace thus loaded is called, is thick and horny. The ephippia may be 

 observed in winter,floating about in the water, often in abundance. (See plate 

 IX.) 



Daphnia Pulex. 



Bibliography, — Monoculus pulex, Lmnceus, Sys. Nat. 10 Ed., i., 635, No. 4, 1758. 



Gm.elin, Syst. Nat. 13th Edit., i., 2999, No. 4. 



Poda, Ins. Mus. Grsecus, 124. 



Muller, Faun. Insect, Fredrichsdalens, 95. 



Blumenbach, Handbuch der Naturg., 399. 



• Manuel, Enc. nieth., VII., 722, No. 15, t. 265, f. 1-4. 



Fahricius, Entoml. Syst., ii., 497. 



Leach, Encyc. Brit. art. Entoml. 



-^ Jurine, Hist, des Monoc, 85. 



Cuvier, Tab. Element., 455. 



Daphene pulex, Muller, Zool. Dan. Prod., 199, No. 2400, 1776. 

 Daphnia pulex, Latreille, Gen. Cvust. et Ins.; Hist. Nat. gen. 



et part., des Crust; R^gne Anim; Cuv. 

 Lamarck, Hist. Nat. des An. s. Vert. Edit.|^2, V., 



181, No. 1. 



Lamouelle, British Insects, 81. 



Straus, Mem. der Mus. d'Hist. Nat., v. t. 29. 



, Demarest, Consid. g6n. sur les Crust., 372, t. 54. 



Baird, Ann. Nat. Hist., i., 254. 



M. Edwards, Hist. Nat. des Crust. 



Guerin, Iconograph. Crust., t. 33. 



Daphnia pulex, 0. Fahricius Faun. Greenland., 263. 

 Leach Edm. Encyc, vii. art. Crustaceol. 



