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fertilisation can take place, and the spermatozoon obtain 
access by the micropyle to the germinal spot. When the air- 
chamber has been filled with water the outer covering of the 
egg hardens and becomes elastic; it is no longer soft and 
adhesive,* or, as the Americans term it, “it frees.’? In this 
paper it will be unnecessary to enter further into the embry- 
ology of osseous fishes, neither will it be required to prove that 
the elements for respiration must be received through the outer 
coat from the surrounding water. Here, however, it becomes 
necessary to point out that as oxygen has to be imbibed 
through the outer covering of the egg, certain mechanical 
influences may be at work to prevent this necessary absorption, 
and so to decrease or altogether cut off the necessary aération. 
In some fishes the breathing chamber is very large, swelling 
the egg to as much as double its original size, and it is evident 
that were these eggs fixed close together prior to distension, 
one of two things must occur, either their due expansion must 
be checked by one pressing against another, or some must give 
way. 
I have already mentioned the eggs of the common smelt, 
which possess filaments that adhere to contiguous objects, if 
these filaments are torn off the egg dies. A number placed 
together prior to imbibition give the appearance under the 
microscope after the air chamber has become filled that they 
are honeycombed, which is due to the number of facets the 
egos show owing to pressure one against another. Irrespective 
of injury due to pressure, it is obvious that due aération of the 
yelk will be stopped, and as a result death will ensue, a subject 
I will not pursue further here. 
The period which fish eggs take incubating is not only 
exceedingly varied among those of closely allied species, but it 
is likewise affected by many extraneous causes. Hggs of sea 
fishes, as a rule, would appear to hatch in a shorter period than 
* Rawsom has observed of the eggs of the trout, pressed from the parent 
into water, stick to the dish for a time, but if first left exposed to the air 
for a little while, do not. In the stickleback the breathing chamber was 
complete in five minutes after impregnation, and the funnel of the micro- 
pyle was effaced in fourteen minutes. 
