462 
DR. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
the micropyle is what its position and structure suggest, viz. to admit the spermatozooids 
to the surface of the yelk. 
It may be here mentioned, although it adds little to the strength of the evidence 
adduced, that ripe eggs yet within the ovisacs cannot be impregnated. All attempts to see 
the spermatozooids in the breathing-chamber failed ; nor is this to be wondered at, as the 
funnel of the micropyle dips so deeply into the pit in the granular opaque discus proli- 
gerus, that it is impossible to see its apex clearly until it is withdrawn to some extent ; 
thus the first moments of the entry of the spermatozooids are lost, and their extreme mi- 
nuteness and delicacy, as compared with the egg, add to the difficulty of the observation. 
It was observed during these experiments that the spermatozooids continued to move 
freely for twenty minutes or more in the viscid layer, but became still very soon if 
they had first to float a very short distance through water. The surer plan therefore is 
to apply the testis while only a little moisture covers the egg, and afterwards to fill the 
cell with water. 
d. Relation of these sequences to the surrounding medium and to the Spermatozooids . — 
An accident occurred during these observations which shows how well the spermatozooids 
continue to move in the viscid secretion of the oviduct. Eggs yet within the parent fish 
were unintentionally fertilized by applying forceps which had just before held a piece of 
testis to the sexual orifice of the female. 
I was thus led to make an experiment with a view of ascertaining what share water 
had in inducing the changes which follow impregnation. 
I fertilized the ova yet in the oviduct of a three-spined female, by applying to the 
sexual aperture a fragment of testis from a ripe male. In ten minutes some of these 
eggs, pressed out and examined without water, were found to have a concentrated discus 
germinativus, and the yellow droplets had disappeared from the cortical layer; the 
breathing-chamber was not, however, distinct, partly in consequence of the strong refrac- 
tion of light, partly from its small size ; but on adding water it was at once apparent, so 
promptly, indeed, that it must have been present before. The fish was then covered 
with oiled silk and put aside, and eggs pressed from her twenty-eight minutes after im- 
pregnation were found contracting. Forty-eight minutes after they were still con- 
tracting, and then water was added, under observation, to see if it increased the activity 
of the movements, but such result was not observed. Two hours and a quarter after, 
more eggs, pressed from the fish, were just about to cleave. Water being then added, 
to make the object more distinct, the funnel of the micropyle was seen dipping into the 
deep pit of the discus germinativus, thus proving how imperfectly the yelk-sac had 
distended. 
Five of these eggs which had not touched water were put into pure nut-oil twenty 
minutes after impregnation ; five minutes later they were seen contracting, and at two 
hours ten minutes after impregnation four out of the five were cleaving. Thus concen- 
tration of the formative yelk, formation of a small breathing-chamber, and even cleavage 
may occur without the presence of water, if maternal fluids are present. But I ought 
