THE WATER-FLEA. 481 
The FAtRY-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, branchiz, 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 cf the 
pool. 
“Tt is certainly the most beautiful and elegant of all the Entomostraca. The male is 
especially beautiful. The nninterrupted 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 antennze, and its bright red tail, with the beautiful 
plumose sete 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 Cladécera, or Branch-horns, because their antennze 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 antennze, and the lower pair are used in swimming. In the first 
family, the Daphniadze, the lower antenne 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 W ATER-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 antennee 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. Ifa 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 
Vou. U1.—61. 
