THE AETinCIAL INCUBATION OF OVA. 51 



From 40° to 45° is the best medium temperature. 

 A greenhouse is a very good place in the winter 

 for early operations, because a fair equable tem- 

 perature is kept up ; but if the early spring be 

 warm and sunny it is obviously the worst place 

 possible, as it is not easy to keep down the heat. 

 Although light is required for the attendant, it is 

 not required, nay, it is most undesirable for his 

 charges, imless they are perfect fish ; and so delicate 

 is the organization of the eye in the alevias that they 

 cannot bear the light, and the trays, therefore, should 

 always be kept covered, save when under examina- 

 tion. The exclusion of light has also the effect of 

 checking confervoid, or other growths. I here give 

 a plan which has occurred to me of keeping down 

 the temperature of the water, when the weather 

 becomes warm, which I think will in use be found 

 very effective. It is not desirable by any means to 

 attempt to cool water by putting ice into it. In 

 the first place, ice water is not advantageous to the 

 fish; in the second, the dropping of lumps of ice 

 into the water wOl induce sudden changes of tem- 

 perature, which are very undesirable. Now, I would 

 have a refrigerator, say of about double the size of 

 the trays, but shaped somewhat like a tray, for the 

 water to pass through after it leaves the cistern, and 



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