THE WATER-FLEA. 481 



The FAIRY-SHRIMP is appropriately named, as a more fairy-like creature can hardly be 

 conceived. It is to be found in several parts of Europe. 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 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." 



BRANCH-HORNS; CLADOCERA. 



WE now come to some of the minute species of these curious animals. The creatures 

 belonging to this order are termed the Cladocera, or Branch-horns, because their antennae 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 antennae, and the lower pair are used in swimming. In the first 

 family, the Daphniadse, the lower antennas 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 horse- 

 ponds, which are so trodden about by cattle that they seem to consist of equal parts of bad 

 pea-soup and duck-weed, are favored 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 color 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 round the pond, thus obeying some strange 

 instinctive command that, though inaudible to human ears, is conveyed to the myriads whom 

 it concerns, and marshals their hosts with the same wonderful discipline that governs a flock 

 of starlings. If a shadow should fall upon this belt of Daphnias, they all suddenly vanish, 

 and appear again as soon as the darkness has passed away. 



The eggs of the Daphnia are placed within the space between the shell and the body, and 

 are there kept until they are hatched, and the mother permits them to escape from under her 



VOL. IIL-6L 



