1906] THE EcGs OF THE FRESH-WATER LING. 223 
fully develop. The ova of the ling are, indeed, more delicate and 
more susceptible to unfavorable conditions than those of the cod. 
and haddock.’’ Now, these observations would apply exactly to 
the present egg. It is so light that the slightest movement in 
the water carries it hither and thither. In still water it falls to 
the bottom, and, indeed, unlike marine eggs, which are in water 
of greater specific gravity, the egg of the fresh-water ling cannot 
permanently float. Itis perfectly spherical and has a diameter of 
1°77 mm. (=.0695 inch) and the globular oil sphere measures 
. -354 mm. (=.039 inch) in diameter. The egg of the marine ling 
measures 1.68 mm. (=.066 inch, or even .og16 inch) in diameter 
and the oil globule .g6 mm. (=.037 inch), so that the fresh-water 
species produces an egg in general of smaller size, indeed in pro- 
portion, it may be said to the different size reached by the full 
grown form in both species. Whereas the burbot reaches a 
length of only 12 to 30 inches and a weight (according to Pennell) 
of 2 to 8 pounds; the marine ling may measure 24 to 72 inches in 
length and a weight ranging from 15 to 60 pounds. 
None of the burbot’s eggs were fertilised, so that no germinal 
disk was formed, though a thin layer of protoplasm surrounded 
the ball of clear yolk fluid. The yolk was not granular, and the 
bright globule of oil lay free in the yolk and moved readily about 
as the egg revolved when pushed by a scalpel on the stage of the 
microscope. In some of the eggs a thin irregular envelope of 
protoplasm collected round the globule, but in most examples it 
was not present. A perivitelline space separates the yolk-globe 
trom the thin capsule of the egg. The capsule itself is a simple 
transparent shell, as in all pelagic types of ova; and in optical 
section it appeared as if double, and concentrically striated—a 
false effect—but repeated and careful examination showed radial 
striations in the thin capsule; these striations apparently corres- 
ponding with minute dots or pits occurring all over the exterior. 
The micropyle showed the usual features, a slight conical thicken- 
ing in the centre of which was the ‘aperture seated in a crater-like 
depression. As in the case of the marine ling, the eggs of this 
fresh-water form are delicate in the extreme, and very readily 
