460 
DE. W. H. HANSOM ON THE OVUM OF OSSEOUS FISHES. 
seen to be closed ; a fragment of testis from a ripe male was applied to the edge of the 
glass cover, so that the spermatozooids came at once into contact with the viscid layer. 
They were then watched incessantly, for about eighteen minutes, and seen vividly 
moving in contact with all other parts of the yelk-sac, except near the micropyle within 
the area pressed upon by the glass cover. My attention was then withdrawn ; seventeen 
minutes later they were languidly moving in the same parts, twenty minutes later they 
were nearly all still ; the pressure was continued till two hours twenty-five minutes after 
the testis had been applied, when no signs of impregnation appeared, and the next day 
the egg was addled. 
Experiment 2. — Two ova were then impregnated in a similar manner, for control, 
without pressure. The breathing-chamber was distinct in each in three minutes and 
a half, and vivid contractions of the yelk began in eleven minutes. 
Experiment 3. — An egg was strongly pressed, in such a way that the micropyle being 
in profile, was not closed ; the spermatozooids were seen in active motion quite near to 
the aperture, and the evidence of impregnation was discoverable before removing the 
pressure in the changes which the cortical layer underwent, although no breathing- 
chamber could be seen until the pressure was removed. This egg went on to cleavage, 
although it was later than normal, and the cleavage masses were irregular. This expe- 
riment was intended to show that pressure alone, if it does not close the micropyle, 
does not prevent impregnation. 
Experiment 4.— I put seven eggs into a larger but otherwise similar cell, and applied 
pressure so that the cover flattened an area of each egg the diameter of which was equal 
to half that of the egg. To these eggs I carefully applied the testis from a vigorous male 
on two occasions: and the spermatozooids were seen actively moving during the twenty-five 
minutes I watched, but I could find no indications of impregnation having occurred. I 
then removed the pressure and applied a fresh piece of the testis, and in three minutes 
five of the seven eggs showed a breathing-chamber. Of the two failures, one at least 
had its micropyle so placed that it might be closed by pressure against another egg 
(Plate XVI. fig. 34), and the other had it looking downwards in such a position on the 
inclined stage of the microscope, that the current would tend to carry the spermatozooids 
away from it. 
Experiment 5. — I put four eggs of Gasterosteus pungitius (which are clearer and rather 
better for this inquiry than those of the three-spined species) into the cell without pres- 
sure and fertilized them. I watched closely one egg, which was placed with the mi- 
cropyle in full face, so that the aperture at its apex was well seen. Spermatozooids 
were seen approaching and entering the funnel, and one was watched till it disappeared, 
apparently in the direction of the interior of the egg, just at the moment when it seemed 
to occupy the aperture at the apex of the micropyle. Immediately after, the depth of 
the funnel began to diminish, and a breathing chamber commenced to form ; two or three 
more spermatozooids were less distinctly seen playing about in the apex of the funnel as 
it was shortening : one of these appeared to become still before it vanished, apparently 
