Ill GENERATION OF FISHES AND THEIR FECUNDITY /I 



looking somewhat like grains of chalk. If the roe of a 

 spawning fish is examined it is seen that some of the eggs have 

 become larger and transparent, while a portion of the roe still 

 consists of the chalk-white smaller eggs. In fact, the eggs 

 become more or less clear and transparent when they are ripe, 

 and then they become loosened from the sides of the roe, fall into 

 the cavity, and so make their way to the exterior. 



The difference between the unripe and the ripe egg is due to 

 a change in the condition of the yolk, which becomes more liquid 

 and less granular. But there is a still earlier condition of the 

 egg in which there is no yolk at all. In this condition the egg 

 consists really of germ only, and is a minute mass of trans- 

 parent living substance. The formation of the yolk commences 

 some months before the spawning season, and the presence of 

 opaque eggs in the roe, of eggs which have the appearance of 

 separate grains to the naked eye, is a sure sign that the fish 

 would have spawned in the following season. In small fish 

 however, and in large fish some time after the spawning season, 

 the roe is usually found to be quite small and, when cut open, to 

 show no appearance of distinct grains. It appears soft and 

 contains only the very young eggs in which no yolk has been 

 formed. It is often said of fish in this condition that they have 

 no roe in them, but the roe though small is always present, and 

 accurate knowledge of the changes through which it passes is 

 very necessar)/ in considering the question of the age and size at 

 which fish begin to breed. 



The generative organs of the male fish are very different in 

 structure from those of the female. In the herring and nearly 

 all other bony fishes the male organ, milt as it is sometimes 

 called, testis as naturalists call it, is a solid body. That is to say, 

 it is not a sac with a large internal cavity like the roe, but when 

 cut through appears to be a mass of substance without cavities, 

 although of a soft nature and when ripe full of liquid. It is 

 really composed of a number of tubes which join with one another 

 like the tributaries of a river until a single tube is reached which 

 opens to the exterior with that of the opposite side by a single 

 aperture (Fig. 31). In consequence of the number of these 

 tubes the testis has really a spongy structure, and the liquid milt 

 is produced in the tubes, and pressed out at the external opening 

 into the water in the spawning process. The milt mixes with the 



