HISTORY OF THE EGG FROM FERTILIZATION TO CLEAVAGE. 17 



of a similar kind, which may now be described. Figs. 1-4 Plate XXVI.. 

 illustrate what was seen. The egg was taken from the fish and fer- 

 tilized in the live-box. under the microscope. The egg was placed in 

 a drop of water on the object-glass, and another drop containing sper- 

 matozoa was placed on the inner face of the cover-glass. The cover of 

 the box was then adjusted, and the whole placed in a position for observa- 

 tion under the microscope, tilted to the horizontal plane. The cover was 

 then gradually 'pushed down until the two drops came into contact. The 

 egg had lain in water about five minutes before the opportunity for fer- 

 tilization was given. Twenty minutes later the conditions presented 

 were those of Fig. 1. The micropyle was a little eccentric, and its inner 

 end in contact with a pointed elevation of the blastodisc. The perivitelline 

 space had already attained a considerable depth, and the disc looked as 

 if suspended by a point that could not get away from the micropyle. Five 

 minutes later (Fig. 2), the polar globule came into view at the month 

 of the micropyle, and at the end of fifteen minutes more (45 minutes 

 after fertilization) the disc broke away from the micropyle (Fig. 3), and 

 at once its upper surface assumed its even regular contour. At the 

 moment the point of contact was broken, the polar globule bounced suddenly 

 away from the micropyle, like an elastic ball released from pressure, and was 

 soon out of sight. The second polar globule was not seen ; but there 

 can be but little doubt that it was left in the micropyle at the time the 

 disc snapped its connection and the first globule was liberated. This 

 seems all the more probable, as the first cleavage began only five minutes 

 after the rocket-like escape of the first polar globule, and as fifteen 

 minutes elapsed between the appearance of this globule and its escape. 

 The polar globules are quite transparent, and their presence in the 

 micropylar canal would not be easily detected with a low power. 



The movement of the first polar globule may have been due to its 

 elasticity and sudden release from compression ; but it seems not improb- 

 able that it was propelled by a quick stroke of the egg membrane, given 

 at the moment of its recovery from the pull to which it must have been 

 subjected while the disc remained attached to the micropyle. 



In this connection, the sudden apparent reduction in length of the 

 micropyle, on its release from the egg, is worthy of notice. During con- 

 tact the micropylar funnel measures 15-20 p. in length (Fig. 2, PI. XXVI.); 

 a moment after the connection is broken, its length is but a trifle more 



