GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 155 



there appears near the surface of them a small homogeneous 

 body. This element, which appears like a spot or a clear 

 space, is formed by a mass of protoplasm, devoid of granula- 

 tions. This space enlarges slightly and becomes the centre 

 of a radiated figure, a little sun, from which rays, the 

 length of which gradually increases, spread out in every 

 direction. These rays are nothing but lines along which the 

 yolk-granules are arranged. If the clear space is carefully 

 examined, it is seen to contain a small homogeneous cor- 

 puscle. This has nearly the same refractive power as the sur- 

 rounding protoplasm which makes it a little difficult to see. 

 Sometimes Her twig has seen a delicate line start from this 

 corpuscle, pass to the periphery of the egg, and become con- 

 tinued into a little filament floating in the perivitelline liquid. 

 The clear spot changes its place; it gradually approaches the 

 centre of the yolk and goes to meet the nucleus of the egg, 

 which also reaches the centre of the vitelline sphere. The 

 two bodies finally meet near the middle of the egg. The 

 homogeneous corpuscle contained in the clear space which 

 comes from the periphery appears to be formed of the same 

 substance as the nucleus of the egg, and is, like that, coloured 

 by carmine. Hertwig calls it a small nucleus — measuring 

 4ju, while the nucleus of the egg is not less than 13,u. The 

 nucleus of the egg changes its shape, executes amoeboid move- 

 ments, grows, and is soon surrounded by the clear protoplas- 

 mic substance which comes from the periphery ; finally, it 

 becomes fused with the little nucleus and from the fusion of 

 these two nuclei arises the first cleavage-nucleus. While 

 these last modifications are being accomplished, the radiated 

 figure remains ; it even extends, and becomes still more clearly 

 marked ; it involves all the yolk. The nucleus of the egg, 

 and the little peripheral nucleus which becomes attached to 

 it, both surrounded by a layer of transparent protoplasm 

 without granulations, occupy the centre of the stellate figure. 

 Since the clear space near the periphery of the egg appears 

 constantly five or ten minutes after the eggs have been mixed 

 with the spermatic fluid, Hertwig does not hesitate to con- 

 sider the formation of this space as the result of fecundation. 

 The small homogeneous body which he has found to exist 

 there is the head of a spermatozoon ; the filament which 

 starts from it is the tail of the same The head of the sperma- 

 tozoon is one of the two nuclei which meet and conjugate ; for 

 this reason Hertwig calls it the spermatic nucleus (Sperma- 

 kern). The first cleavage-tiucleus is then the product of the 

 fusion of the nucleus of the egg (Eikern), which is only the 

 original germinal spot, with the spermatic nucleus (Sperma- 



