DIPS INTO MY AQUARIUM. 



85 



Reproduction is of two kinds. Two sorts of eggs are pro- 

 duced by the female : — Summer eggs, from ten to half a hundred 

 being deposited in an open space between the valves of the 

 carapace, where they He till the young are ready to be hatched ; 

 and winter eggs, two only in number, which are placed in what is 

 called the saddle, on the back of the carapace, where they remain 

 till hatched by the returning warmth of spring. 



It will be known to most of my readers that nearly all Crusta- 

 ceans undergo several metamorphoses during their development. 

 The majoritv of the Cladocera emerge from the egg in a matured 

 form ; but Sars, of Christiana, has made the interesting discovery 

 that in winter the larva leaves the egg in the form of a nauplius in 

 the case of Leptodora^ one of the primitive members of this group. 

 It would be worth the while of any enthusiastic microscopist to 

 study the development of such forms as Daphnia, for no doubt 

 there is something more to be learned even concerning this much- 

 observed creature. 



We will now take from our gatherings a tiny bit of the pond- 

 weed, of which there is a considerable quantity lying in a tangled 

 mass towards the bottom of the aquarium, or waving in delicate 

 filaments towards the surface. It must be a very small fragment, 

 or we shall probably see nothing properly. Having placed it in a 



small zoophyte-trough or live-cage, we had 

 better examine it first with an inch objective. 

 Here is something worth a good long look. 

 It is a tiny, transparent object, which seems 

 to be moored to a twig, and surmounted by 

 a couple of wheel-like organs, which appear 

 to be constantly revolving. It is at once 

 pronounced to be a Rotifer, or wheel-animal- 

 cule. The fact that it has two wheels makes 

 it probable that we have come across the 

 Common Rotifer {R. vulgaris), which, on 

 closer inspection, it turns out to be (Fig. 5). 

 Having found it, we proceed to examine 

 it with a rather higher power. Giving the 

 ^ig- S-— nose-piece, on which are screwed three 



Common Rotifer, objectives, a slight turn, the half-inch is in 



R. Vulgaris, 



