llf) CRUSTACEA. 



j>oint behind, with the head, which is covered by a shield-like 

 plate, exposed ; the antennae are two in number, very large 

 and branched. They have ten legs. (Daphnia, &c.) 



In the genus Daphnia (Mullcr), the head is distinct, and 

 produced beneath into a kind of snout, furnished with a 

 single central small eye. From each side of the head arises 

 a large antenna-like organ, having a long basal joint, 

 at the extremity of which each antenna is divided into 

 two long articulated branches, each of which supports 

 a number of long bristles. The functions of these organs 

 in swimming, (being, in fact the only external apparatus 

 employed in this motion), has induced M. Strauss to regard 

 them as forelegs, although it is evident, asMullerand Jurine 

 observed, that they represent the upper antennae of the ty- 

 pical crabs. Within the shell of the Daphnia are to be ob- 

 served ten small leg-like organs, having the second joint vesi- 

 cular, the eight anterior ones being terminated by a dilated 

 joint, margined with hairs, and serving as oars. By a curi- 

 ous provision the eggs are deposited in a dorsal kind of pouch 

 beneath the shell within which they are hatched ; at the end 

 of the fifth day the young have acquired sufficient power to 

 take care of themselves, and are expelled by the female. 



These animals, of which there are numerous species, are found 

 in fresh and standing water, where they swim about with very 

 great agility, their large branching antennae giving them a curious 

 appearance. Their history has been traced, notwithstanding their 

 minute size, by several eminent observers : the works of M <!.-. 

 Schaeffer, Ramdohr, Strauss, and the elder Jurine may be espe- 

 cially mentioned. It has been observed, that a single impregna- 

 tion is sufficient for several (six or more) generations. Occasion- 

 ally these insects abound in water to such a degree as to impart 

 to it their own tint ; and, as one of the species is of a red colour, 

 the hue thus imparted to the water has been supposed to have 

 been caused by blood. The type of the genus is the species above 

 mentioned, or the Monocultis pulex Linn. It is about one-twelfth 

 of an inch long, and in spring is of a red colour, which towards 

 summer becomes rosy, but at other seasons it is of a greenish 

 white colour. It is very abundant. 





