2 U. S. BUREAU OF FISHERIES. 



harmful, and a certain amount of loss is probably due to them. 

 Keighard (1890) found that by very careful handling of the eggs at 

 and immediately after fertilization the percentage of eggs that 

 started segmentation soon after fertilization could be considerably 

 increased. Describing the loss met with in the ordinary course of 

 the routine methods, he states that in 252 samples examined 11 per 

 cent had died due to lack of impregnation and 33 per cent due to 

 injury. Unfortunately, although he designates the day and hour 

 at Avhich these observations were made, the age of the eggs is not 

 specifically given. From the context it would appear as 29 hours. 

 It seems that an egg was designated as dead when it showed an 

 opaque white color, a criterion which was adopted also in the present 

 investigation. 



The figures of the losses in ordinary handling of pike-perch eggs 

 given by Keighard are somewhat at variance with those given by 

 L. H. Almy in some unpublished notes on the pike perch. His find- 

 ings and those of the authors follow : 



Almy. 



Age of eggs. 



3 hours 



27 to 29 hours 



2 days 



3 days 



4 days 



5 days 



7days 



9 days 



Per cent 

 loss. 



2.5 

 5.4 

 8.1 

 12.6 

 31.7 

 3.5.5 

 39.0 

 33.4 



Schrader and Schrader 



Age of eggs. 



1 hour 



1 hours 30 minutes 

 8 hours 15 minutes 



19 hours 



29 hours 



2 days 



3 days 



4 days 



5 days 



Per cent 

 loss. 



0.5 

 1.0 

 2.4 

 4.3 

 5.0 

 8.3 

 13.3 

 33.2 

 37.1 



It will be seen that in contrast to the 33 per cent of white eggs 

 given by Eeighard, Almy observed only 5.4 per cent at 27 hours, 

 while our own observations are lower still. Almy's and our figures 

 agree fairly well, the latter being lower up to two days and a trifle 

 higher at four days. It is not quite clear to what such a discrepancy 

 could be due, although Reighard's hypothesis of injury as a cause 

 of mortality would, of course, itself allow for large differences on 

 account of the varying skill and care bestowed on the eggs. (Tem- 

 perature conditions were in all cases apparently the same, the water 

 being in the neighborhood of 45° F.) Keighard describes the in- 

 jury as taking place most easily over the oil globule, and there is 

 no reason to dispute the observation. However, the following ex- 

 planation which he advances to account for this phenomenon does 

 not seem to rest on a very firm physical basis (Keighard, 1890, pp. 

 33, 34) : 



In the natural position the yolls sphere lies with its lower half against the 

 egg membranes. These membranes, therefore, support this half of the yolk, 

 surrounding it as if it were resting at the bottom of a cup. The upper half 

 of the yolk is, on the contrary, not of the same form as the investing membrane ; 

 its spherical surface is interrupted by the protruding oil globule. 



The result of this arrangement is that when any pressure is brought to bear 

 on the egg membranes, so that the space within which the yolk lies is reduced, 

 the yolk is able to resist this pressure by fitting itself against the egg mem- 

 brane at every part of its surface except over the oil globule. The strain, 



