642 ENTOMOSTKACA : APUS ; BRANCHIPTJS ; AKTEMIA. 



nearly so commonly as the Entomostraca already noticed. It is 

 recognized by its large oval Carapace, which covers the head and 

 body like a shield ; by the nearly cylindrical form of its Body, 

 which is composed of thirty Articulations ; and by the multiplica- 

 tion of its Legs, which amount to about sixty pairs. The number 

 of joints in these and in the other appendages is so great, that in a 

 single individual they may be safely estimated at not less than two 

 millions. These organs, however, are for the most part small ; and 

 the instruments chiefly used by the animal for locomotion are the 

 first pair of Feet, which are very much elongated (bearing such a 

 resemblance to the principal Antennae of other Entomostraca, as 

 to be commonly ranked in the same light), and are distinguished 

 as Rami or Oars. With these they can swim freely in any position; 

 but when the Rami are at rest and the animal floats idly on the 

 water, its Fin-feet may be seen in incessant motion, causing a 

 sort of whirlpool in the water, and bringing to the mouth the 

 minute animals (chiefly the smaller Entomostraca inhabiting the 

 same localities) that serve them as food. — The Branchipus stag- 

 nalis has a slender, cylindriform, and very transparent Body of 

 nearly an inch in length, furnished with eleven pairs of Fin-feet, 

 but is destitute of any protecting envelope ; its head is furnished 

 with a pair of very curious prehensile organs (which are really 

 modified Antennae), whence it has received the name of Cheiro- 

 cephalus ; but these are not used by it for the seizure of prey, the 

 food of this animal being vegetable, and their function is to clasp 

 the female in the act of copulation. The Branchipus or Cheiro- 

 cephalus is certainly the most beautiful and elegant of all the 

 Entomostraca, being rendered extremely attractive to the view 

 by "the uninterrupted undulatory wavy motion of its graceful 

 branchial feet, slightly tinged as they are with a light reddish hue, 

 the brilliant mixture of transparent bluish -green and bright red of 

 its prehensile antennae, and its blight red tail with the beautiful 

 plumose setae springing from it : " unfortunately, however, it is a 

 comparatively rare animal in this country. — The Artemia salina 

 or ' Brine Shrimp ' is an animal of very similar organization, and 

 almost equally beautiful in its appearance and movements, but of 

 smaller size, its body being about half an inch in length. Its 

 ' habitat ' is very peculiar ; for it is only found in the Salt-pans or 

 Brine-pits in which Sea-water is undergoing concentration (as at 

 Lymington) ; and in these situations it is sometimes so abundant 

 as to communicate a red tinge to the liquid. 



502. Some of the most interesting points in the history of the 

 Entomostraca lie in the peculiar mode in which their Generative 

 function is performed, and in their tenacity of Life when desic- 

 cated, in which last respect they correspond with many Rotifera 

 (§ 362). By this provision they escape being completely extermi- 

 nated, as they might otherwise soon be, by the drying-up of the 

 pools, ditches, and other small collections of water which constitute 



