DE. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
463 
to add, that the contractions seemed to be scarcely so vivid as in eggs normally fecun- 
dated. 
With the view of testing whether any changes were due to the mechanical action 
alone of the spermatozooids, I tried to cause the micropyle to be forced by minute 
animalcule, but could not succeed in any instance, in consequence perhaps of the ani- 
malculse being all somewhat larger than the spermatozooids. No better result fol- 
lowed similar attempts with the spermatozooids of Lissotriton punctatus and of Unio 
tumidus. 
If eggs be exposed to water without being fertilized, the viscid layer prevents its action 
to a great extent, for they may be left in it two or three hours without losing their 
flaccidity ; after a still longer time they imbibe a little, even before the viscid layer has 
lost its characteristic properties ; in so doing they become rounded and more tense, the 
yellow droplets become paler, but do not vacuolate : an imperfect concentration of the 
formative yelk occurs. If the unimpregnated eggs be submitted to a stream of water 
of considerable strength, and for some time, by which means a part of the viscid layer is 
removed, although no effect is seen at once, yet in an hour a good breathing-chamber 
appears, and the formative yelk is concentrated. 
Some ill-understood changes take place in the eggs after the death of the parent, which 
diminish the readiness with which they may be impregnated. I kept a dead ripe female 
moist for 1 9f- hours, and found that only five, out of ten of her eggs, could be fertilized, 
although all the ten seemed alike; four hours later, only two out of seven could be 
fecundated. The testis of a male was used successfully after it had been dead twenty- 
one hours. 
If a dead female be kept moist forty-eight hours in summer weather, the eggs inside 
her become a little decomposed, and then a breathing-chamber soon forms when they are 
put into water; the formative yelk concentrating, the yellow droplets vanishing at the 
S,ame time. 
Thus it appears that although in Gasterosteus the formation of a breathing-chamber 
and the concentration of the formative yelk, under normal conditions, only occur after 
fecundation, yet they are only an indirect consequence of the action of the spermatozooids, 
which act by favouring the entrance of the surrounding medium into the cavity of the 
egg- 
2. Later sequences of impregnation. 
a. The yelk contractions are the most striking of the phenomena which follow the 
entrance of the spermatozooids into the egg. They may be watched with a f lens, or 
better, with the compound microscope, using a power of X 50 or X 100, and may be 
spoken of as rhythmic yelk contractions. From the first moment of entry of the sper- 
matozooids, slow contractions of the yelk begin, and assist in the formation of the 
breathing-chamber, causing first a flattening of the surface of the yelk near the germinal 
pole, and afterwards slight changes of outline due to travelling waves at other parts of 
the surface, but not before the breathing-chamber has reached that part. Gradually 
more vivid contractions commence, at various times after fecundation, according to the 
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