MUSEUM OF COMPARATIVE ZOOLOGY. 81 



it will be seen, gives the two cardinal requisites of plenty of air, through 

 the perforated box and loose nettings and a low temperature. 



The very young stages are exceedingly delicate, and their transporta- 

 tion always involves the loss of a large proportion of them, since they 

 cannot stand any considerable disturbance or pressure. The older stages 

 are quite hardy. Great care must be taken in handling the eggs, it being 

 well to float them on and off the netting in water. 



Tliere are several matters that need particular attention in the care 

 of eggs after transportation. They must be placed in a clean receptacle, 

 free from metal, paint, or soluble matter, and in such a way that water 

 can circulate about them. The water, either running or periodically 

 changed, must be: (1) free from foreign substances, so as to prevent 

 the deposition on the eggs of any sediment which would prevent free 

 access of air to the embryo; (2) sufficiently aerated to preserve the 

 embryos alive ; (3) of a temperature which is comparatively uniform, 

 not above 10° C (50° F.) nor below the freezing point. 



In order to place the eggs in such a position that the water can flow 

 around them, they may be put on netting stretched across the receptacle ; 

 however, they will do well on a clean hard surface, such as glass, espe- 

 cially if they are slightly agitated by tilting the dish carefully once a 

 day. But aside from this they should be disturbed as little as possible, 

 and should never be more than a single layer deep. 



The purification of the water is eff'ected by means of filters, which are 

 more essential when the water is turbid, or when one wishes to keep the 

 eggs alive for a long time. The common hydrant water of Cambridge 

 may be used for a short time without filtering, but if it is to be used for 

 five or six days a flannel filter is advisable. 



For more extensive operations, filters of antiseptic " carferal " or char- 

 coal are necessary, because of the presence of small parasites and minute 

 spores, which are very injurious to the eggs. As regards the aeration of 

 the water, it may be said that a simple break in the stream of supply or 

 a dropping of the water is all that is necessary to insure sufficient air for 

 the embryos. Elaborate processes of aeration have been invented, but 

 they are not essential for the limited number of eggs required in labora- 

 tory work. 



The temperature of the water is a very important matter in the care 

 of salmon and trout eggs, for if it rises above 11° C. the life of the embryo 

 is endangered, though at the higher temperatures (below 11° C.) devel- 

 opment is more rapid. 



Cases are known where the time of hatching in cod varied from eleven 



