METHOD OF RECORDING EGG DEVELOPMENT. 191 



short calculation will tell just what eggs are most suitable. Suppose 

 a foreign shipment requiring a two or three weeks' journey is to be 

 made. It is desirable to select the oldest eggs that will arrive before 

 hatching, with a margin for safety besides. By estimating the prob- 

 able temperature of the package, the number of temperature units 

 required for the journey can be readily computed. Thus, if the tem- 

 perature of the package be maintained at about 50° F., in 20 days it 

 will be subjected 20 times 18, or 360 t. u., and if 100 t. u. be allowed 

 for excess in temperature or delay on the journey a total of 460 t. u. 

 is required. By subtracting these 460 t. u. from 900 t. u. it is seen 

 that eggs of an age of 440 t. u. are required — so young that the eye- 

 spot is barely visible when viewed in the ordinary way, but old enough 

 to stand shipment. If this 440 t. u. be now subtracted from the read- 

 ing on the day of shipment, the remainder corresponds to the reading 

 of the day on which the required eggs were taken. Eggs for long for- 

 eign shipments are especially difficult to select, and any evidence 

 corroborative of the exact age of the eggs at a time when mistakes are 

 particularly to be avoided is very gratefully received. 



In handling quinnat-salmon eggs at Baird Station it is safe and 

 practical to pick them till they have an age of 100 t. u., when they are 

 carefully picked for the last time before entering the tender stage. 

 It is not thought that the entrance on this stage involves any sudden 

 transformation, but the eggs are believed to increase daily in sensi- 

 tiveness from the time they are taken until a time when, with the 

 apparatus employed, it is no longer safe to handle them. After enter- 

 ing the tender stage they are left undisturbed until the germ disk has 

 completed its growth around the egg. In the *' summer run" eggs 

 this occurred very close to 225 t. u. At this time it was found safe to 

 uncover them; that is, to raise the baskets gently until the contained 

 eggs are near the surface of the water and then suddenly, but care- 

 fully, to lower it, thus forcing the water up through the eggs and 

 removing any accumulations of sediment that may have been depos- 

 ited upon them, until they are clean or nearly so. Sediment usually 

 collects only upon the upper layer of eggs. In performing this opera- 

 tion care must be taken to allow all the eggs to settle before it is 

 repeated. After they have been treated in this manner for several 

 days and have an age of about 300 t. u., they are quite out of the 

 tender stage and may be subjected to daily pickings, the same as older 

 eggs. 



In observing eggs from time to time while in the tender stage the 

 most striking phenomenon and the one most readily seen with the 

 unaided eye is the ring or loop which defines the germinal layer in its 

 growth around the egg. This ring is visible to the unaided eye as 

 early as the sixth day, at 57° F., or at an age of 125 t. u., as seen in 

 fig. 6 of the accompanying sketches, when it is apparently not yet 

 fully formed. It retains its circular shape until it passes the equa- 



