634 THE WATER-FLEA. 



The figure of the young Brine-shrimp, which is greatly magnified, is introduced for 

 the purpose of showing the great dissimilarity of form in the young and the adult. 

 Indeed, through the whole of the Entomostraca, the young bear a great general resemblance 

 to each other, but are quite unlike their parents. 



THE two larger figures represent the FAIRY-SHKIMP, appropriately named, as a more 

 fairy-like creature can hardly be conceived. It is to be found in several parts of England, 

 and there is a pond on Blackheath where it used to be tolerably common. In spite of its 

 comparatively large size, measuring more than an inch in length, it may easily escape 

 observation, as its body is of glassy transparency, and scarcely visible in the water except 

 by the red and blue tints of its tail, branchiae, and feet. It always inhabits stagnant 

 water, and may even be found in the half putrid mass of mud and water that lies at 

 the bottom of casting nets. 



In his valuable work on the British Entomostraca Dr. Baird gives the following 

 account of this beautiful creature : "They swim upon their back, and in fine, warm weather, 

 when the sun is not too strong, they may be seen balancing themselves as it were, near 

 the surface, by means of their branchial feet, which are in constant motion. On the least 

 disturbance, however, they strike the water rapidly with their tail from right to left, and 

 dart away like a fish, and hasten to conceal themselves by diving into the soft mud, or 

 amongst the weeds at the bottom of the pool. 



It is certainly the most beautiful and elegant of all the Entomostraca. The male is 

 especially beautiful. The uninterrupted undulatory waving 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 beautiful plumose setae springing from it, render it exceedingly attractive to 

 the view. 



The undulatory motion of its branchial feet serves another purpose in addition to that 

 of keeping the animal suspended in the water. The thorax or body of the animal has 

 been described, when floating on its back, as like the cavity of a little boat, the feet 

 representing the oars. When these are in motion, they cause the water contained in this 

 cavity to be compressed, and to mount up as along a canal, carrying in the current the 

 particles destined for its food towards the mouth. It seems to be constantly, when in this 

 position, employed in swallowing and digesting its food, its masticatory organs being in 

 perpetual motion." 



In the illustration, the upper figure represents the male, and the lower the female. ' 



WE now come to some of the minute species of these curious animals, and, in 

 consequence, all the figures are much magnified. The creatures belonging to this order are 

 termed the Cladocera or Branch-horns, because their antennas are forked and branched. 

 With the exception of the head, the body is wholly enclosed within two shells like the 

 half shells of a walnut. There is only one eye, of very large comparative size ; there are 

 two pairs of antennas, and the lower pair are used in swimming. In the first family, the 

 Daphniadae, the lower antennae are very large and upper very small. There are five or six 

 pairs of feet enclosed within the shell, and the intestine is straight. 



The common WATER-FLEA is a good example of the typical genus. Eight or nine 

 species of this genus are now known, and the habits are much the same in all. They are 

 to be found in fresh water, whether still or running, but seeming to prefer the former. 

 Even the t horse-ponds, which are so trodden about by cattle that they seem to consist of 

 equal parts of bad pea-soup and duckweed, are favoured residences of the Water-fleas, 

 and several species may sometimes be found in one little pond. 



The common Water-flea has five pairs of feet, the lower antennae branched and 

 branchleted, the lower pair being very large and powerful. The head is lengthened 

 downwards into a prominent beak. These little creatures exist in vast numbers, and 

 sometimes assemble in such heavy masses that they quite change the colour of the water. 

 Dr. Baird has remarked that they will sometimes assemble so as to form a belt of a foot 

 or so in breadth, and ten or twelve yards in length, and that the whole belt will pass 



