152 
BULLETIN OF THE BUBEAU OF FISHERIES 
DEVELOPMENT OF THE EGG 
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CONDITION AT LAYING 
When expressed from the body of the ripe female the eggs are perfect spheres 
2 millimeters in diameter. They are pale yellowish in color and of such transluc- 
enoy as to be easily overlooked in the water. When first laid they are slightly adhe- 
sive, clinging to each other and to surrounding objects, but this quality is lost as 
soon as they are “water hardened”; that is, rendered turgid by the absorption of 
water. 
Like other fish eggs, those of this species are telolethical, the heavier yolk lying 
below the caplike disk of protoplasm, which therefore is seen plainly from above. 
This disk is whitish and covers about half of the surface that can be seen from the 
“animal” pole. (Fig. 1.) At this stage the egg membrane, or shell, everywhere 
rests closely upon the egg and is so thin and colorless as to escape detection easily. 
Its thickness is 15 microns. Of this, the inner zona radiata comprises 9 microns 
and is made up of alternate light and dark bars each 1 micron in thickness. The 
outer layer is very similar to the stratum villosum of the egg of Lepidosteus, described 
by Mark (1890), and is 6 microns thick. The micropyle is easily seen under the 
microscope. At first it is a funnel-shaped depression of the shell, which, w T hen the 
egg is beginning to swell, reaches nearly to the egg proper (germinal disk). A 
very slight implantation cone is seen on the disk opposite it. After 20 minutes in 
water the space between the egg and the shell has swelled so much that the micro- 
pyle dips down but one-third of the distance. By 1^ hours it is withdrawn with 
the shell, now reaching but one-eighth of the intervening distance. The yolk mass 
consists of evenly distributed yolk globules, which, after dehydration, measure from 
8 to 14 microns in diameter. There is no layering of the yolk, as in birds’ eggs. 
No large oil drops are found in the sucker’s egg, but numerous very clear droplets 
of minute size are seen both in the yolk about the edges of the blastodisc and con- 
tained in the cells of the latter after segmentation begins. 
NUMBER OF EGGS LAID 
From one 12-inch female 150 cubic centimeters of eggs, weighing 165 grams,, 
were removed, each egg measuring 2 millimeters across before water hardening. 
By reference to the tables of von Bayer 2 it will be found that this volume contains 
18,000 eggs of this size. Single eggs weigh between 6 and 10 milligrams. A still 
larger female (15 inches long) contained 31,200 eggs. 
SPERMATOZOA 
The sperm cells measure 24.7 microns in length, the ovoidal head or nucleus 
being 5.7 microns. The neck or middle piece is exceedingly small, less than 0.5 
micron, and is seen with difficulty. The nucleus is sometimes blunt at the ends 
but is circular in cross section, resembling that of a trout. It could be seen after 
staining with hematoxylin. The flagellum was evident when iodine was used. The 
2 von Bayer, H.: “A method of measuring fish eggs.” Paper presented before the Fourth International Fishery Congress 
held at Washington, September 22 to 26, 1908. Bulletin, U. S. Bureau of Fisheries, Vol. XXVIII, 1908 (1910), Part 2, pp. 1009- 
1014. Washington. 
