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 morula stage, so 

 called from its likeness to a 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 planula 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 

 dorsalis or noto-chord, which becomes enclosed by the wall of the 

 rest of the organism on either side growing over it. If a 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 

 alimentary 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, except that the germinal vesicle is differentiated as 



