210 THE MICROSCOPE AND ITS REVELATIONS. 



Brancliipus or Cheirocephalus 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 bright red tail with the 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. 



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

 Entromostraca lie in the peculiar mode in which their generative func- 

 tion is performed, and their tenacity of life when desiccated, in which 

 last respect they correspond with many Rotifers ( 452). By this pro- 

 vision they escape being completely exterminated, as they might other- 

 wise soon be, by the drying-up of the pools, ditches, and other small 

 collections of water which constitute their usual ' habitats.' It does not 

 appear, however, that the adult Animals can bear a complete desiccation, 

 although they will preserve their vitality in mud that holds the smallest 

 quantity of moisture; but their eggs are more tenacious of life, and there 

 is ample evidence that these will become fertile 011 being moistened, 

 after having remained for a long time in the condition of fine dust. 

 Most Entomostraca, too, are killed by severe cold, and thus the whole 

 race of adults perishes every winter; but their eggs seem unaffected by 

 the lowest temperature, and thus continue the species, which would be 

 otherwise exterminated. Again, we frequently meet in this group with 

 that agamic reproduction, which we have seen to prevail so extensively 

 among the lower radiata and Mollusca. In many species there is a double 

 mode of multiplication, the sexual and the non-sexual. The former 

 takes-place at certain seasons only; the males (which are often so differ- 

 ent in conformation from the females, that they would not be supposed 

 to belong to the same species, if they were not seen in actual congress) 

 disappearing entirely at other times. The latter, on the other hand, 

 continues at all periods of the year, so long as warmth and food are sup- 

 plied; and is repeated many times (as in the Hydra) so as to give origin 

 to as many successive 'broods.' Further, a single act of impregnation 

 serves to fertilize not merely the ova which are then mature or nearly so, 

 but all those subsequently produced by the same female, which are 

 deposited at considerable intervals. In these two modes, the multiplica- 

 tion of these little creatures is carried-on with great rapidity, the young 

 animal speedily coming to maturity and beginning to propagate; so that 

 according to the computation of J urine, founded upon data ascertained 

 by actual observation, a single fertilized female of the common Cyclops 

 quadricornis may be the .progenitor in one year of 4,442,189,120 young. 



609. The eggs of some Entomostraca are deposited freely in the 

 water, or are carefully attached in clusters to aquatic Plants; but they 

 are more frequently carried for some time by the parent in special recep- 

 tacles developed from the posterior part of the body; and in many cases 

 they are retained there until the young are ready to come-forth, so that 

 these animals may be said to be ovo-viviparous. In Daphnia, the eggs 



