THE SPAWNING AND DEVELOPMENT OP THE COD-FISH. 217 



circumstance may account for the fact that the male fish during the act 

 of spawning generally swims deeper than the female ; and likewise for 

 the fact that the micropyle is located uear the lower portion of the egg, 

 while with other fish which have heen observed this order of things is 

 reversed. After the egg has floated in the water for some time, it under- 

 goes a very striking change. At the lower end the yelk becomes 

 thicker, aud viewed from the side appears like a crescent-shaped edge, 

 of a deep yellow, and much more compact than the rest of the yelk. 

 This compact mass grows constantly more distinct, till at last it forms 

 a tolerably large semicircular projection. The yelk has thus secreted 

 those parts which are to serve in the formation of the young fish from 

 the remainder, which is to serve as its food. This portion, however, 

 has still to undergo considerable changes till it is fit to produce the 

 young. At the same time one cau observe how the oil-bladders, which 

 were originally scattered over the whole surface, gradually flow together 

 and form larger bladders, gathering in a close circle round the micro- 

 pyle, and so growing together form a transparent circle round it. These 

 changes take place both in the impregnated and in the uuimpregnated 

 egg. The first visible effect of the impregnation takes place after the 

 lapse of a few hours. In the middle of the disk a faint furrow is seen, 

 which gradually becomes deeper, till at last it divides the disk into two 

 symmetrical halves. After this furrow has become somewhat less 

 marked, another one appears in each of the halves, striking the first one 

 perpendicularly, by which process the disk is divided into four divisions 

 of a spherical shape. Each one of these is again divided, so that there 

 are eight divisions, and these again into sixteen, thirty-two, sixty-four, 

 &c„ divisions. Finally the disk becomes divided into so many divisions, 

 and these divisions become so small, that the surface of the disk seems 

 just as smooth as at first. With this process the first period in the devel- 

 opment of the egg terminates. It has continued about four days, (112 

 hours.) Nothing as yet can be seen of the foetus, and the disk has only 

 just been prepared to produce it. 



The second period commences by the disk's upper side, which is turned 

 towards the yelk, and whicli till then has been quite flat, rising like a 

 watch glass in the direction of the yelk, so that it assumes the shape of 

 a strongly convex lens, one half of which stretches into the yelk, while 

 the other half is outside. In the middle it has a thin circular rim, 

 outside of which numerous small globular bodies can be discerned, 

 arranged like a wreath round it. These seem to be some of the small 

 particles produced by the last dividing process, which have been 

 loosened from the disk and are floating about in the clear oily border 

 surrounding it. When that part of the disk which is protruded into 

 the yelk has reached its greatest height, which is often much greater 

 than the outer part, it begins to collapse, but in such a manner that the 

 process is completed more rapidly on one side than on the other. At 

 this place it becomes more compact, and here it is that the foetus is 



