32 REV. MOSES HARVEY ON 



protected. Heuce it comes that, as a rule, the fish which carry a large uumber of ova are 

 iu reality less prolific than those which carry a much smaller number of eggs, as a much 

 larger proportion of the latter survive to maturity. An enormous proportion of the cod 

 ova perish from their extreme delicacy and minute size. For the same reason, the artificial 

 hatching of cod ova is difficult, and requires very delicate manipulation. 



When in the hatchery, the cod ova are to be fertilized artificially, the female is taken 

 from the tank in which they are kept till ripened, and held over a vessel partially filled 

 with pure sea-water, iu such a position that the weight of the ovaries presses iipon the 

 canal. The ova then run freely into the water iu the vessel, without any pressure on the 

 stomach of the fish The male fish, having ripe milt, is then taken from the water and 

 held over the vessel iu a similar manner, till the required milt has mingled with the ova. 

 The fish are put back into the well or tank as soon as " stripped," to await further ripening, 

 the period over which the process goes on being five or six weeks. The water containing 

 the ova and milt is then gently stirred and left standing until the spermatozoa have 

 entered the microphyle, a minute opening in the membrane surrounding the eggs. 

 Having entered the ova, the spermatozoa do not disappear into the yolk, but form from 

 their head or nucleus, the male pronucleus which meets and fuses with the female 

 pronucleus, as the germinal vesicle is termed. "Fertilization depends upon the conjuga- 

 tion of these two sexually differentiated nuclei." From this conjugation-nucleus, formed 

 by the fusion of the male and female nuclei, the new being takes its origin. A single 

 spermatozoon is capable of fertilizing an egg. 



When thus fertilized the eggs are cleansed, measured, so as to ascertain their number, 

 and placed iu the hatching apparatus for^ further development. The quantity of water, 

 ova and milt must be duly proportioned to each other, in order to secu.re the fecundation 

 of the egg. 



After fertilization, the first real development of the embryo commences by the process 

 of segmentation. In an unimpregnated egg, the germinal layer which covers the yolk 

 appears like a transparent substance containing numerous minute vesicles. When the 

 process of impregnation first takes place the egg turns a dull colour, but speedily brightens 

 again, and the luimerous minute vesicles become larger biit less numerous, because they 

 become confluent and unite. One hour after impregnation the protoplasmic layer can be 

 seen travelling in beaded streams towards the lower pole of the egg, where the germinal 

 disk is forming. The first mysterious life-movements have begun. In water having a 

 temperature of 40', three hours are reqviired before the germinal disk becomes defined, 

 and the protoplast extending from it is seen to embrace the yolk. 



About six hours after impregnation, the segmentation of the germinal disk can be 

 seen, by the aid of a microscope, to have commenced ; and the egg, which originally 

 consisted of one cell, is divided into two cells, through the shortest or equatorial diameter. 

 Segmentation advances gradually by the two first cells dividing themselves and forming 

 four new ones. Each of these again divides into two, and thus a multitude of small cells 

 come into existence. Twenty-four hours after impregnation, segmentation has advanced 

 so far that the germinal disk is divided into fifteen cells, and the nucleus can be seen 

 through the cells. In two days the process in the cleavage of the disk is still further 

 advanced and about sixty new cells can be counted, forming four layers, one over the 

 other. As the segmentation goes on the cells become by the fourth day more and more 



