30 



EXPERIMENTS IN THE IMPREGNATION OF PIKE- 

 PERCH EGGS. 



By Herschel Whitaker, of Michigan. 



The eggs of the wall-eyed pike, after having been for 

 some time in water, measure about two millimeters (aliout 

 l-12tli of an inch) in diameter. The egg has an en velo ping- 

 membrane (or zona radiata) of the usual form. Outside 

 this is a second thinner membrane, which wrinkles and 

 stains more deeply in the haematoxylin than does the 

 inner zona radiata. The eggs are very adhesive, and it is 

 to this outer membrane that the adhesiveness is due. 

 There is j)robably also a third membrane within the zone, 

 but this has not been determined with certainty. Within 

 these membranes is the yolk, having a diameter of 1.4 mm. 

 (about l-18th of an inch). The yolk is spherical, and in 

 one side of it is imbedded a spherical oil -drop having a 

 diameter of .8 mm. (about 1-31 st of an inch). The oil- 

 drop causes the surface of the yolk-sphere to protrude to 

 one side. The oil-drop being lighter than the yolk, is 

 always turned upward, so that in looking at the egg from 

 above the oil-drop appears to be in the middle of the yolk, 

 while in looking at the egg from the side the oil-drop 

 appears to be at the toj) of the yolk. 



I shall speak of that pole of the yolk in which the oil- 

 drop is imbedded as the upper pole, and of the opposite 

 side as the lower pole. A line drawn about the yolk, half 

 way between these two ]3oles, will be spoken of as the 

 equator. When the egg is at rest the lower pole of the 

 yolk rests upon the egg membranes, so that the space 

 which separates the yolk from the zona is altogether above 

 and at the side of the yolk and oil-drop. This space may 

 be spoken of as the breathing space. Surrounding the 

 yolk and oil-drop is a layer of protoplasm, which farms an 

 investment for them and separates them from t]ie water in 

 the breathing space. 



