160 OVARIES OF FISHES. 
The cases in which I found only yolkless ova in spent ovaries were 
recognised as spent, like the dabs in the same condition described 
by Mr. Holt, by the presence of the remains of ripe eggs in the 
ovarian cavity. Are there cases in which, these remains having been 
expelled, nothing is left to distinguish a fish that has recovered from 
spawning from one that has never spawned? I have no evidence 
by which to answer this question conclusively, but it is certain that 
ovaries which are known to have previously spawned, from the pre- 
sence of degenerating yolked ova, are sometimes no larger than others 
which are, from the absence of any indication to the contrary, set 
down as immature. For instance, in a plaice, 143 inches long, the 
spent ovary was 2 inches, and the end of it 44 inches from the end 
of the ventral fin, while in a specimen 13} inches long, apparently 
immature, the ovary was 3 inches long and only 4 inches from the 
end of the ventral fin. To avoid this possible uncertainty in dis- 
tinguishing immature fish it would be advisable, in order to ascertain 
the limit of size at which maturity commences, to examine a large 
number of specimens within a short space of time—one month for 
example—in the middle of the spawning period. At this time there 
would be no mature specimens in which yolk had not commenced to 
develop, and no spent specimens which had reverted to the resting 
condition. 
Dab. 
I have not studied the dab in the spent condition, but I have 
found that the formation of yolk certainly commences in some 
specimens in September. I killed one specimen 114 inches long on 
September 18th; the ovary was 2% inches long, 33 inches from 
the end of the ventral fin. The yolk formed a thin layer of very 
small granules in the extreme outer region of the egg, and was not 
sufficient to diminish its transparency to any great extent. The 
diameter of the largest of the yolked eggs was'17 mm. In some of 
the ova under microscopic examination the membrane of the germinal 
vesicle was seen to be shghtly wrinkled. The appearance of one of 
the eggs is shown in Fig. 3, 
Flounder. 
Mature flounders examined in January had ovaries in an advanced 
condition. In February many were ripe. In July I killed two from 
the aquarium which were known to have spawned in the spring. 
One was 11 inches long, the ovary was flaccid and rather large,and did 
not resemble an immature ovary in external appearance. Micro- 
scopically examined, only yolkless ova were found in the germinal 
tissue, with here and there a shapeless opaque mass, obviously a 
