84 BOARD OF AGRICULTURE. 



layer of club-sliaped Ijodies (granular layer) ; witliin tliis a 

 layer of transparent albuminous matter (Tona puUucida) ; 

 still more internally the spherical yolk granules, among which 

 lie the g-erminal vesicle with its germinal spot. 



Until fertilized it is incapable of change. The ftrst indica- 

 tions of development are shown in the segmentation of the 

 yolk into two equal masses, of these into four, of those into 

 eight, and so on, the numbers doubling each time from the 

 binary segmentation of each cell until the yolk is largely in- 

 creased in bulk, and presents a uniform mass of granules, and 

 a smooth investing membrane. At the commencement of this 

 segmentation of the yolk, the germinal vesicle and spot disap- 

 pear, and in the mammalous ova has hitherto eluded all attempts 

 to trace it, thougii it has been pointed to as the centre of this 

 work of segmentation and increase in the yolk. At the same 

 time the spermatozoa can be seen in the membranes surround- 

 ing the yolk, and even in the yolk itself, as may readily be seen 

 in the rabbit's ovum, taken sixty hours after connection with 

 the buck male. 



When the segmentation of the yolk is completed, there appear 

 new developmental changes at one point of its surface, and in 

 the membrane (germinal membrane) investing it. This con- 

 sists in a thickening of the membrane in the form of an ovoid, 

 in tiie centre of which the rudimentary elements of the young 

 animal soon become apparent. 



We have thus glanced at the main points of the phenomenon 

 of impregnation. AVe have traced the steps resulting in the 

 union of two living elements, derived from different animals, 

 incapable of separate existence, but potent when coml/med not 

 only to lay the foundation of a living being, but to insure that 

 this being shall develop the qualities of the male and female from 

 which it sprung, alike in form, size, color, vigor and power of 

 enduring hardships, constitution, mental powers, and even pro- 

 clivity to disease. This point must never be forgotten in con- 

 nection with subsequent developments, that here, in the initial 

 stage of the individual existence, all the characters of the future 

 animal are determined by the unseen but not the less real prop- 

 erties of those two simple germinal structures — the ovum and 

 spermatozoon. These have no less individuality and character 

 than the animals from which they sprung, and as the ovum and 



