lo The Ottawa Naturalist. 



seem to absolutely require, for their welfare, subjection to a 

 temperature almost as low as freezing point. They also survive, 

 as we have seen, extremes of dryness. It would appear from 

 Carl Semper's experiments that the eggs of Arteinia must be 

 be both dried and frozen before they will pass through their 

 normal embryonic changes. Thus does Nature exhibit to us 

 her strange paradoxes ! The two most hurtful and fatal influ- 

 ences, so far as the eggs of most aquatic animals are concerned, 

 appear in the Phyllopods to be the necessary and most favor- 

 able conditions for development. Under these conditions the 

 eggs may remain for lengthy periods without hatching out. 

 Semper, for example, obtained eggs of Arteinia in dry mud in 

 1872, but the young brood did not hatch out for five years. 

 Branchipus eggs were kept in like manner, in dry mud, from 

 1867 until 1877, and after this long period of dessication, and 

 apparent dormancy, produced the nauplii, or young of Bran- 

 chipus, in the normal manner. Experiments of this nature with 

 the eggs o{ Lepidoptera and other Arthropods ended always in 

 fatal results. It is a curious fact that the eggs of Branchipiis 

 flourish under great extremes of temperature. They will freely 

 hatch out in any temperature between 32° F. and 86° F.; but at 

 the latter temperature the young nauplii emerge in about 

 twenty-four hours, whereas at a point midway (58° F.) they take 

 several weeks to hatch. 



With such wonderful powers of endurance, so far as its eggs 

 are concerned, it is no matter of surprise that Branchipus thrives 

 in the shallowest ponds — mere rain-pools in fact — which are 

 frozen into solid sheets of ice, or dried up into cakes of hard 

 mud. Each winter and each dry summer sweeps away the 

 whole race of adults : but the eggs survive as fine dry dust. The 

 mummified and frozen eggs are caused to hatch when the appro- 

 priate season comes, though several seasons may elapse before 

 the new generation bursts forth from the shell. Intense summer 

 heat or an unseasonable return of frost may suddenly cut off the 

 brood in the midst of their activity ; but their eggs sink into the 

 underlying mud, and endure for one or for many seasons until 



