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. 



llie 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 Avhole 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. Svi^am- 

 merdam was the fii'st 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 Dr. 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. f 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. judex. 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 Merrctt perhaps is an exception to this remark. See above, p. 63. 



