STRUCTURE OF DOMESTICATED ANBIALS. 303 



laid. lu order to examine it, therefore, a hen must be killed 

 and the egg must be observed during its passage through the 

 oviduct, when on the surface of the yolk, and on the surface 

 only, furrows are marked as if made with a nail. These far- 

 rows are multiplied crossways, and then cross ways again, and 

 this process is repeated until the whole surface is changed 

 into these same globular bodies, already noticed in the rabbit 

 and dog, but which in the hen extend only over a small part 

 of the surface of the yolk. Now this small part of the surface 

 of the yolk is that white speck which is seen at once when you 

 open the shell of an egg ; and from it the chicken is de- 

 veloped. 



In fishes, there is still another process. Suppose we take 

 the salmon. The first segmentation of the yolk consists in 

 halving and quartering, and then the process of self-division 

 goes on only in one-half, viz., in the upper half of the yolk, 

 the lower half undergoing no change, so that you have at 

 first only two spheres, one below and one above, then two in 

 the upper part, then four in the upper part, then eight in the 

 upper part, then sixteen in the upper part, the lower part re- 

 maining in its primitive condition, and the whole upper part 

 finally being transformed into a body similar to what we have 

 as a whole in the mammal, resting as it were on a cup of un- 

 altered, unchanged yolk in the lower j)art. In the fish, it is 

 this mulberry-like, segmented portion of the yolk which is 

 changed into the germ, while the other half takes no part in 

 the formation of the germ, but only feeds it, being in fact ab- 

 sorbed into it. The egg is actually a live being, only it is a 

 live being which struggles into its structure by its own activ- 

 ity ; — and in the formation of the organs it afterward pos- 

 sesses, the process of growth is not one of enlargement 

 simply, but involves such changes as to transform a uniform 

 mass into a variety of systems built of different tissues and 

 endowed with special functions. In the chicken, two parallel 

 swellings first arise along the middle line of the back, leaving 

 a shallow furrow between themselves and the white disc 

 spoken of above as a white speck, enlarges and spreads, so 

 as to cover the whole surface of the yolk visible from above. 

 If you look at this furrow in a section it will be something 

 like an arch, open above. Gradually this furrow grows wider 



