186 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



protoplasm of the yelk into the structures of the growing embryo would 

 be very marked in consequence of subjecting young shad to a tempera- 

 ture of 55° F. By this means, reasoning from what we know of the 

 other phases of develoi^ment when exposed to like temperatures, the 

 absorption of the yelk might be retarded so as not be completed for six 

 or seven days. This would give us, added to the maximun i^eriod of 

 incubation of nine days at 53° F., a total of fifteen days, a period cer- 

 tainly long enough for all practical purposes in the transportation of 

 young fish for stocking purposes. 



I would seize this opportunity to remark that it must, however, be 

 borne in mind that the growth of an embryo in the egg is different from 

 the growth of the young animal after it has been hatched and begins 

 to feed. The fish embryo has a store of food, which is inclosed in the 

 yelk-sack, which can scarcely be said even to be transformed, it only 

 suffers a change of place, as particle after particle of the yelk substance 

 is removed and built up into the structures of the growing embryo. 

 This transfer is effected through the blood, and also by apposition from 

 below. The young growing animal in feeding must truly transform the 

 protoplasm which it eats; it must digest it; it is carried into the blood 

 as chyle, and so to all j^arts of the body to repair the waste incident to 

 the exhibition of life. The two processes, upon careful comparison, are 

 wholly unlike. A fall in the temperature diminishes the rate at which 

 this transfer of the yelk substance to the structures of the growing em- 

 bryo takes place. The frequency of the pulsations of the heart decreases, 

 consequently the yelk substance which is in contact with vascular sinuses 

 below the embryo is not taken into the blood as rapidly. The result of 

 all this is that the absorption of the yelk is impeded and made to min- 

 ister to the development and growth in size of the young fish for a 

 longer period. 



A few other points, and I have done with this part of the subject for 

 the present. Most steamships now use fresh water distilled by an appa- 

 ratus specially constructed for the purpose. This water, i^rovided the 

 most ordinary care was exercised in the storage, would be well fitted 

 to use in the process of retardation. The eggs carried on the trays 

 ought to be occasionally sprinkled with iiure sterilized water. The 

 distilled water supi)lied aboard steamships answers this description 

 fully, and almost everything is accordingly ready to our hands. To 

 reduce the temperature of the water used in the latter stages of devel- 

 opment, when it would be necessary to transfer the eggs to water, say 

 on the eighth day, or .after they had been for eight days on the damp 

 trays, it would be desirable to avoid contamination of the water from 

 the ice. To avoid this, the water should pass through coils of block-tin 

 pipe, placed in tubs, and kept filled with cracked ice ; thus we could 

 lower the temperature to at least 60° to 58° F. The same water 

 might be used several times over, because with care it would be so 

 slightly contaminated with organic matter that putrefactive processes 



