148 How to obtain it. 
seems a wonderful provision of nature for enabling man to 
collect eggs and carry them at once hundreds of miles by rail, &c., 
to the hatchery if needed. I have known them nearly forty-eight 
hours on a journey without taking harm, but after the first twenty- 
four hours the sooner they are laid down in the hatching apparatus 
the better. 
A fully developed unimpregnated ovum consists of a mass of 
protoplasm, in which, a little to one side, may be seen a small 
clear nucleus or cell called the germinal vesicle, and which in its 
turn contains a still smaller cell or nucleolus—the germinal spot. 
Some hours after being taken from the fish and laid on the grilles, 
the germinal vesicle in each egg may be seen on the portion of 
the ovum which is uppermost, and, should such an ovum be 
fertilized by spermatozoa, great changes soon take place, the first 
of which is, that the cell consisting of the germinal vesicle and 
germinal spot is split into two cells, each of which in its turn 
forms two, and so on in geometrical progression, which simple 
cleavage, known as segmentation, continues for some time. At the 
end of this process the ovum is a mass of nucleated corpuscles 
without cell walls, and has reached the second or moru/a stage, so 
called from its likeness toa mulberry. The cells on the surface 
of this mulberry mass gradually become elongated or column 
shaped, ending in long threads of protoplasm called cilia, by 
means of which it can not only move through the fluid but 
produce currents in it in its immediate neighbourhood. The 
ovum has now reached the third or p/anuda stage. At this point 
a groove appears, down the centre of which a white streak, soon 
taking the form of a ridge, may be seen, which is the chorda 
Gorsalis or noto-chord, which becomes enclosed by the wall of the 
rest of the organism on either side growing over it. Ifa section 
be made through this embryo, three layers—an outer, a middle, 
and an inner—may be easily distinguished by the aid of a 
microscope. From the outer layer, the skin, brain, and spinal 
column, are developed; from the inner, the lining of the 
ailmentary canal with its appendages; whilst the middle layer 
forms the rest, which is by far the greatest part of the organism. 
When an ovum has not been impregnated it remains 
unchanged, excepting that the germinal vesicle is differentiated as 
