456 
DE. W. H. EANSOM ON THE OVUM OE OSSEOUS EISHES. 
eight hours in carmine. Neither can they serve for admitting the spermatozooids, both 
because they are, if examined in ripe ovarian ova, full of a semisolid vacuolating matter ; 
and because the micropyle exists as in other osseous fishes, and in the same position, 
marking the germinal pole. It is interesting to note that the eggs in the mass of 
spawn are all so placed that the micropyle looks directly towards the inside of the col- 
lapsed tube which forms the band. One effect of this arrangement must be to prevent 
its occlusion by contact. 
In perch spawn, taken from the river, the micropyle is easily seen, after letting out 
the young embryo with a needle ; a deposit of fine mud being usually deposited in the 
furrows around it, thus rendering it visible to the naked eye. 
The dotted sac has a structure in all essential particulars like that of Gasterosteus 
(Plate XYI. figs. 32 & 33). 
The river Bullhead (Cottus Gobio). 
The eggs are held together by a viscid secretion of the oviduct, the yelk-sac is 
furnished with a micropyle surrounded by button-shaped processes, just as is seen in the 
allied genus of Gasterosteus. 
The Gudgeon (Cyprinus Gobio). 
The egg has a micropyle at its germinal pole, consisting of a conical pit perforated 
at its apex. The dotted yelk-sac is villous on its outer surface. The villi are soft, 
tenacious, easily deformed by pressure. The unimpregnated eggs imbibe water, form 
a breathing-chamber, and the formative yelk concentrates without exhibiting any active 
contraction. 
The Minnow (Leuciscus phoxinus). 
The eggs have a micropyle similarly placed, with a raised margin around the mouth 
of the funnel. In water they act just like those of the gudgeon, except that some very 
slow changes of the form of the yelk-ball occur. 
The Chub (Leuciscus cephalus). 
The egg has a similar micropyle, the margin of the funnel is crenated, and its sides 
are furrowed, it reacts in water like that of the gudgeon. 
The Impregnated Ovum. 
The Stickleback. 
I purpose first to describe the changes which follow fecundation, up to the time at 
which the yelk commences to contract, then to relate the experiments made to show 
