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we may perceive certain structures, as shown in a magnified 
form in the diagram on the wall of the egg of the stickleback. 
Around the eggs before they are deposited and holding the 
mass together, is a viscid layer or secretion from the oviduct of 
the female. This secretion will for some time resist the imbi- 
bition of water in the unimpregnated ova, so that they have 
been observed to remain flaccid at least two and a half hours 
after immersion. Subsequently it seems to set round the eggs, 
making them cohere firmly together. 
The egg itself may be said externally to have a double 
cortical layer, the two being divided by an interspace. The 
outer of these (which is rather thick) may be termed the yelk 
sac, and is in immediate contact with the second internal or 
vitelline membrane which surrounds the yelk ball within the 
yelk sac. The outer membrane of the egg is distinguished in 
one spot by a number of cup-shaped or mushroom-like pro- 
cesses which cover about one fourth of its surface and mark 
the germinal pole. In the centre of these small elevations is 
the micropyle, consisting of a funnel-shaped pit, directed 
towards the centre of the egg and continued inwards as a 
narrow tube, with the inner end open. This outer covering of 
_ the egg is changed by the imbibition of water from an easily 
_ torn membrane into a firm elastic one. The yelk-ball, or that 
_ portion surrounded by the vitelline or inner membrane, contains 
_ those essential portions of the egg which are subsequently 
directly transformed into the germ, and into which the 
micropyle opens. Between the two layers I have described is 
_ aspace, small in the unimpregnated egg prior to the imbibition 
_ of water, but which becomes filled, forming what has been 
termed the breathing chamber, a space increased probably also 
in size by a contraction of the yelk. In the stickleback this 
% absorption of water from the outside commences near the 
in most osseous fishes, observes Ransom, water enters 
f 
freely through the yelk sac, and the breathing chamber 
E. commence eee at all pare aa the Nanri It 
