314 History of British Entomostraca. 
Habits, manners, $c The insects which belong to this genus are 
to be found both in the fresh water and the sea. The fresh water 
species abound in the muddiest, most stagnant pools, and in the clear- 
est springs, and the ordinary water with which the inhabitants of 
London are supplied for domestic purposes, contains them often in 
great numbers. The marine species are to be found, often in immense 
abundance, in small pools on the sea shore, within high water mark, 
living amongst the sea weeds and corallines, which frequently fringe 
so elegantly the beautiful little wells and clear round pools which 
are hollowed out in the rocks by the sea shore, and are equally abun- 
dantly to be met with in the open ocean, where, by the curious lu- 
minous properties they possess, they assist in producing that beau- 
tiful phosphorescent appearance of the sea, which has so much puz- 
zled naturalists to discover the cause of. It is amazing, when we 
examine the pools of water which are to be met with in our fields, 
or sea shores, to find such infinite myriads of little creatures sport- 
ing about in all the enjoyment of existence and it is exceedingly 
curious and interesting to know the extraordinary fertility of such 
apparently insignificant creatures. Specimens of the quadricornis 
are often to be met with carrying thirty or forty eggs on each side,* 
and though the other species which have only one external ovary, 
do not carry so many, still the number is very considerable. Ju- 
ririe has with great fidelity watched the hatching and increase of 
the quadricornis in particular, and has given a calculation which 
shews the amazing fertility of the species. He has seen one female, 
isolated, lay ten times successively but in order to be within bounds, 
he supposes her to lay eight times within three months, and each 
time only forty eggs. At the end of one year this female would 
have been the progenitor of 4,442,189,120 young ! ! The first mo- 
ther lays forty eggs which at the end of three months, at eight 
layings during that time, would give 320 young. Out of this num- 
ber he calculates 80 as males, (there being in every laying a great 
proportion of females,) the remaining 240 are females. The follow- 
ing table will then shew the prodigious extent of their fecundity :t 
* Leeuwenhoek says, that in the specimens which occurred to him of the 
quadricornis, he counted the eggs to be three or four in breadth and nine or ten 
in length. Epist. ad. Soc. Reg. Ang. p. 138. 
f- Jurine, Hist. des. Monoc. &c. p. 32. 
4 
