78 
BRITISH ENTOMOSTRACA. 
third moulting ; and gradually after that increase in size, 
lose their transparency, become continuous, and form a 
dark mass on the outer edge of the intestine, partly globular 
and partly elongated. At the sixth segment of the body, 
the ovary communicates with the open space on the back 
of the animal already described, and immediately after 
the fourth moulting, we see the eggs already laid and 
deposited in this space, where they remain till fully 
hatched. 
The animals belonging to this family are only to be 
found in fresh water, generally in ponds and ditches ; 
some preferring those in which there is much of the 
lemna, or duckweed, floating on the surface, others 
delighting in horseponds where cattle come to drink. In 
such places they are often to be found in myriads, and 
almost the whole year round ; and as they sometimes 
in some species assume a red colour, they have been said 
to have tinged the water with the hue of blood. Swam- 
merdam was the first who observed this ; he says he has 
seen them in such numbers at Vincennes, as actually to 
give the water of a horsepond the colour of blood ; and 
he quotes a friend of his in Holland, a Hr. Schluyl, who 
had noticed the same in one of the canals near his house. 
This statement has been repeated by Derham, * and by 
many others, upon Swammerdam's authority, but not, as 
far as I know, from personal observation.! I have, how- 
ever, frequently seen large patches of water in different 
ponds assume a ruddy hue, like the red rust of iron, or 
as if blood had been mixed with it, and ascertained the 
cause to be an immense number of the D. pulex. The 
myriads necessary to produce this effect is really astonish- 
ing, and it is extremely interesting to watch their motions. 
On a sunshiny day, in a large pond, a streak of red, a foot 
broad, and ten or twelve yards in length, will suddenly 
appear in a particular spot, and this belt may be seen 
rapidly changing its position, and in a very short time 
* Physico-Theology, p. 364, note a; Glasgow, edit. 1745. 
f Merrett perhaps is an exception to this remark. See above, p. 63. 
