206 How to obtain it. 



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 quadricoruis. 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, quadricornis. 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- 

 FJ 2 ages attached to the sides of their 



Cyclops quadricornis, enlarged. bodies towards the tail. TheSC 



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 

 progess through the water by means of a quick succession of 

 jerks. The sexes may be distinguished by the form of the 

 antennae, 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 



