ENTOMOSTRACA. 557 



and in Daphnia, " Water-fleas," the head is protruded be- 

 yond the shell. In Polyphemidce the head is large, and 

 almost entirely occupied by an enormous eye, giving the 

 creatures a most singular appearance ; the Monoculus is 

 a well-known example of this group. Another family, 

 not provided with a shell or carapace, called Branchio- 

 2ioda, from the name of the typical genus, Branchiopus 

 stagnalis (fig. 255), is often found after heavy rains in 

 cart-ruts and other small pools. 



Daphnia pulex is found commonly in fresh water, and 

 is scarcely inferior to its marine relative, Talitrus locusta, 

 in agility. The Corophium longicorne, remarkable for its 

 long antennas, is not less so for its singular habits. It 

 is found at Eochelle, where it burrows in the sand, and 

 wages constant war with all other marine creatures of 

 moderate size that come in its way. 



Dr. Baird has followed up the successive generations in 

 Daphnia pulex ; so far as the fourth change in the Daphnia 

 born from the ordinary ova, and so far as the third in those 

 born from the ephippial eggs. These ephippia, or " winter 

 eggs," require a few words of explanation. They are, in fact, 

 eggs covered with envelopes of more than usual hardness 

 and thickness, being enabled to withstand an excess of 

 cold, which would surely prove fatal to the parent. This 

 observer found, upon examining ponds which had been 

 filled up again by the rain after remaining two months 

 dry, numerous specimens of the Cyclops quadricornis in 

 all stages of growth. Dr. Baird, in his " Natural History 

 of British Entomostraca," 1850, tells us that they have 

 many enemies. 



" The larva of the Corethra plumicornis, known to micro- 

 scopical observers as the skeleton larva, is exceedingly rapa- 

 cious of the Daphnia. Pritchard tells us they are the choice 

 food of a species of Nais ; and Dr. Parnell states that the 

 Lochlevin trout owes its superior sweetness and richness of 

 flavour to its food, which consists of small shell-fish and En- 

 tomostraca." These animals abound both in fresh and salt 

 water. Artemia? are formed exclusively in salt water, in salt 

 marshes, and in water highly charged with salt. " Myriads 

 of these Entomostraca are to be found in the salterns at 

 Lymington, in the open tanks or reservoirs where the brine 



