7 s BRITISH I-.NTOMOSTKAl A. 



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 In- 

 found in fresh water, generally in ponds and ditches ; 

 some preferring those in which there is much of the 

 Icmna, 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 Yincennes, as actually to 

 give the water of a horsepond the colour of blood; and 

 he quotes a friend of his in Holland, a Dr. Sehluyl, 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 Swamnu'i-dam's authority, but not, as 

 far as I know, from personal obser\ation.f I have, how- 

 ever, frequently seen large patches of water in di IK -rent, 

 ponds assume a ruddy hue, like the red rust of iron, or 

 as if blood had been mixed witli it, and ascertained the 

 cause to be an immense number of the I). /i/>/i',r. The 

 imriads necessary to produce this ellect is really astonish- 

 ing, and it is extremely interesting to watch their motions. 

 On a snnshhn da\, in a large pond, a streak of red, a loot 

 broad, and ten or t\ve!\e \ards in length, will suddenly 

 appear in a particular spot, and this belt may be seen 

 rapidly changing its position, and in a very short tune 



1 Physico-Theologj;, p. 364,notea; Glasgow, edit. i;r>. 



f MCMVII |i<Tliap> is an c\cc|.iii.n to tins remark. tScc above, p. 63. 



