THE SPAWNING AND DEVELOPMENT OF THE COD-FISH. 215 



till tlie time for spawning arrives, when they frequently assume such 

 enormous dimensions that the term '* fish-mountain," which is sometimes 

 applied to them, does not seem exaggerated. In all these schools, even 

 in those which come first, the male and female fishes are intermingled, 

 which but rarely occurs among other kinds of fish. Thus, as to the 

 herring, the female fishes always come first, and are followed by the 

 males, which pour their milt over the roe. This peculiarity in the cod- 

 fish is easily explained by the above-mentioned character of its roe ; 

 thus, in order that an impregnation may take place, the roe and the 

 milt must be poured out at the same time and mix in the sea. In those 

 fishes which arrive first, the roe and the milt, although tolerably devel- 

 oped, are as yet far from being matured. The roe is still so small-grained 

 that without the microscope the small eggs can scarcely be distinguished. 

 These eggs are of a light yellowish-red color, and show under the micro- 

 scope a very light outer ring, and an inner opaque fine-grained mass, 

 (yolk.) All the eggs in this stage are connected by a fine texture full 

 of blood-vessels, mostly in irregular, conical processes, all which con- 

 verge toward the center of the roe-bags. These encircle an inner hollow, 

 into which the eggs are received as soon as they are .matured, in order 

 to be carried out through the two longer channels, which start from the 

 inner side of the roe-bag, and which unite toward the back in one. In 

 their further development the eggs constantly increase in size, and, at 

 the same time, become more transparent, till they are almost colorless. 

 They are now almost mature, but still loosely connected by a thin texture, 

 and surrounded by a thin covering, in which the feeding blood-vessels 

 spread in a branch -like manner. Soon, however, this covering bursts, 

 and the mature egg is now cut off from its conuectiouwith the rest, and 

 falls into the inner hollow of the roe-bag, from which, by a gentle press- 

 ure on the fish's abdomen, it can be brought out through the sexual 

 opening (poms genitalis). The eggs are now as transparent as water, 

 about one millimeter in diameter, and appear to the eye like small pearls 

 of clear crystal. Placed in a glass with sea-water, they first sink to the 

 bottom, on account of the downward movements of the water, but rise 

 again, as soon as the water has become calm, to the surface, where they 

 form a closely -packed floating layer. Their specific weight is less than 

 that of the sea-water, and greater than that of fresh water, of which 

 fact one may easily be convinced by placing them in a glass of common 

 drinking-water, in which they rapidly sink to the bottom, without rising 

 again.* The yelk of those eggs which have but recently come out from 

 the ovarium appears, under the microscope, quite clear and transparent, 



* Tins accurately-measured specific weight is of the greatest importance for the 

 development of the egg. If, for instance, it should storm and rain for several days, 

 there might easily be formed a thin layer of mixed sea and fresh water, which would 

 contain less brine ; so that if the specific weight of the roe floating in the sea were 

 only a small particle less, this circumstance would have a very injurious effect on its 

 development. 



