142 THE CANADIAN NATURALIST. [April, 



liatching-boxes, will be covered with a peculiar parasitical plant, 

 Leptomitus clavatus, which gives them the appearance of being 

 wrapped in cotton. These should be removed, as though the 

 other eggs will not be immediately infected, yet the fibres of this 

 vegetable growth will in time get around them, and prevent the 

 water having free access to them, when they too will die. The 

 unfruitful salmon-eggs should be at once removed ; but when the 

 ova are very small, as is the case in trout, &c., it is better to wait 

 till the parasitical plant has appeared before removing " the tares 

 from the wheat," as the operation can then be performed more 

 easily. It is therefore much better not to have a layer of small 

 stones at the bottom of the case, as many of the ova will sink be- 

 tween them, and from remaining unperceived may in time cause 

 great damage. It is true that the salmon instinctively makes a 

 hole, and covers her ova with small stones. But she, in all proba- 

 bility, only adopts this precaution in order to protect them against 

 their numerous foes, and not that the development of the embryo 

 may be thereby in any way accelerated. 



It might not unnaturally be supposed that it is best to trans- 

 port the ova in the same element as that in which they are depos- 

 ited in the ordinary course of things, viz., in water. But it must 

 at the same time be remembered, that every fertile egg contains a 

 living being, which requires a constant supply of air for its preser- 

 vation, and that the quantity of air contained in a confined vessel 

 is more rapidly consumed by the ova than fresh air can be absorbed 

 from the surface. The consequence will be that unless fresh 

 water be constantly supplied, or the water in the vessel be by some 

 means aerated, the embryo contained in the egg must die. But 

 not only will the constant replenishing the vessel with fresh water 

 be troublesome, and often impossible, but it will also be attended 

 with great risk to the safety of the ova. 



If it is borne in mind that it is not the water, but the air which 

 is therein contained, that is essential to the preservation of the 

 ova, it will be apparent that if they be kept moist, and have a con- 

 stant supply of fresh air, the necessary conditions will be obtained. 

 The readiest and easiest way is to pack them in damp moss (the 

 marsh moss, Sphagnum, which absorbs moisture like a sponge, is 

 the best), through which the air will readily circulate.^ 



* Professor Rasch told me that he has hatched ova in damp moss, 

 without even immersing them in water at all. 



