206 How to obtain tt. 
under favourable conditions its rate of increase is considerable, 
the females usually producing three broods per month. The 
females are often very abundant, but the males are usually some- 
what scarce. Unfortunately frost seems to be speedily fatal, the 
next year’s insect developing from the epphipial, or winter egg as 
it is commonly called, contained in the parent at death. At 
Gremaz, in France, this difficulty is said to have been overcome. 
Each species or variety of Daphnia possesses five pairs of legs, 
- whilst the body is made up of eight segments, and the stomach 
can be distinctly seen. 
Scarcely second in importance is another minute crustacean, 
Cyclops quadricornis. In general outline it somewhat suggests a 
small lobster, excepting the claws, which are substituted by four 
long horns, from which it gets its name, guadricornis. They are 
found naturally inhabiting very 
much the same places as the 
water fleas, but they are very 
different looking creatures, being 
of a whitish appearance, and the 
females may readily be distin- 
guished by two curious append- 
ene ages attached to the sides of their 
Cyclops quadricornis, enlarged. bodies towards the tail. These 
are the ovaries or egg sacs, and 
they are very prominent objects. The males are without them, 
but the females are by far the most numerous, and both sexes 
progress through the water by means of a quick succession of 
jerks. The sexes may be distinguished by the form of the 
antenne, which vary in each, as well as by the presence or 
absence of the egg sacs. : 
The great importance of these creatures will be understood, 
when we consider that it has been estimated that a single female 
may be the origin of over four hundred millions of its species in 
one year ; nay, according to a calculation by Jurine, a single 
Cyclops is capable of producing over four billions in the course of 
a single year. The calculation is based on the assumption that 
all live, and go on producing, but in reality, such an occurrence 
never takes place, as there are so many predacious animals which 
