26 
BRITISH ENTOMOSTRACA. 
upon the edges of the ponds, and nearly on the surface 
of the water, but in stormy or cold weather they are no 
longer to be seen.” They can swim as freely upon their 
back as on their inferior surface, and in both these posi- 
tions we may see their feet continually in motion, alter- 
nately from below upwards, and from right to left, 
fatiguing the eye to follow them. Indeed their branchial 
feet seem never at rest, for when the animal no longer 
uses its rami, but floats idly on the water, these organs 
are still in rapid motion, causing a sort of whirlpool in 
the water, and attracting towards their mouth the objects 
floating about them. Their chief food appears to be the 
smaller species of Entomostraca, which generally are 
found in great abundance in the same places, such as 
Daphnise and Cy prides, the shells of which latter little 
creatures they can easily break down by means of their 
strong mandibles. Schceffer says they perish very quickly 
after being taken out of the water, or when the ponds 
dry up. It appears, notwithstanding, that after a pond 
has been dried up for some time, and suddenly filled anew 
by heavy rain, in two days these animals will be seen in 
abundance. The eggs certainly retain their vitality long 
after being dried, for these little creatures have been 
known to appear in a ditch that was suddenly filled with 
water after having been dried up for two or three years. 
Frogs seem to be their chief enemy, and they are gene- 
rally to be met with in a more or less mutilated state. 
Professor Retzius, at the meeting of the German natu- 
ralists at Breslau, in September, 1838, announced that 
M. Kollar, of Vienna, had discovered the male of the 
Apus cancriformis , but I have not been able to find any 
detailed description of it.* 
Schoeffer, Berthold, and Zaddach had considered them 
to be hermaphrodites ; but in all probability the males 
will be found, as in the case of the Daphnise, to exist at 
some particular season of the year, and perhaps in small 
* Isis, 1834, p. C80; Froriep’s Kotizen, 1833, pp. 38, 148; Burmeister, 
Organ, of Trilobites, Ray Soc. edit., p. 40, 1846. 
