248 ON THE RELATIONS OF MAN 



The Dog's egg is, in fact, a little spheroidal bag (Fig. 

 12), formed of a delicate transparent membrane called 

 the vitelline membrane, and about T&T to riiyth of an inch in 

 diameter. It contains a mass of viscid nutritive matter 

 the ' yelk ' within which is inclosed a second much more 

 delicate spheroidal bag, called the ' germinal vesicle ' (a). 

 In this, lastly, lies a more solid rounded body, termed the 

 ' germinal spot ' (b). 



The egg, or ' Ovum/ is originally formed within a gland, 

 from which, in due season, it becomes detached, and passes 

 into the living chamber fitted for its protection and main- 

 tenance during the protracted process of gestation. Here, 

 when subjected to the required conditions, this minute and 

 apparently insignificant particle of living matter becomes 

 animated by a new and mysterious activity. The germinal 

 vesicle and spot cease to be discernible (their precise fate 

 being one of the yet unsolved problems of embryology), 

 but the yelk becomes circumferentially indented, as if an 

 invisible knife had been drawn round it, and thus appears 

 divided into two hemispheres (Fig. 12, C). 



By the repetition of this process in various planes, these 

 hemispheres become subdivided, so that four segments are 

 produced (D) ; and these, in like manner, divide and sub- 

 divide again, until the whole yelk is converted into a 

 mass of granules, each of which consists of a minute 

 spheroid of yelk-substance, inclosing a central particle, 

 the so-called ' nucleus ' (F). Nature, by this process, has 

 attained much the same result as that at which a human 

 artificer arrives by his operations in a brickfield. She 

 takes the rough plastic material of the yelk and breaks it 

 up into well-shaped, tolerably even-sized masses, handy 

 for building up into any part of the living edifice. 



Next, the mass of organic bricks, or ' cells ' as they are 

 technically called, thus formed, acquires an orderly arrange- 

 ment, becoming converted into a hollow spheroid with 

 double walls. Then, upon one side of this spheroid, appears 

 a thickening, and, by and bye, in the centre of the area 

 of thickening, a straight shallow groove (Fig. 13, A) marks 

 the central line of the edifice which is to be raised, or, in 

 other words, indicates the position of the middle line of 

 the body of the future dog. The substance bounding the 

 groove on each side next rises up into a fold, the rudiment 

 of the side wall of that long cavity, which will eventually 

 lodge the spinal marrow and the brain ; and in the floor 



