INTBA-OVARIAN EGG OF SOME OSSEOUS EISHES. 55 



stroma of the ovary. The nucleoli (fig. 1, n'.) — there are a 

 great number of them — rest as a rule on the inner surface of 

 the nuclear wall, barring a few, which take up a central 

 position. With an ordinary high power (Zeiss F 4 ) nothing 

 more of an internal structure can be detected. 



The next size (fig. 2) shows a division of the protoplasm into 

 two distinct layers or zones, an outer lighter and an inner 

 darker or more denser one. The egg in this stage is still 

 tolerably transparent. Fig. 2 represents a small gurnard's 

 egg (Trigla gurnardus) 0*030 mm. in diameter. The 

 nucleoli show an inclination to gather still more towards the 

 periphery of the nucleus, and the central portion rarely reveals 

 a germinal spot, while there appears instead an intra-nuclear 

 network which will be more minutely described in larger eggs. 

 In ova of this bulk, and also in somewhat larger ones, one or 

 more of the nucleoli become larger than the others, and in 

 their interior highly refractive specks are visible which have 

 sometimes been described as endonucleoli. Another pecu- 

 liarity about the large germinal spots is that they are always 

 surrounded by a light portion which does not stain with 

 carmine. 



In somewhat larger ova, of a diameter of 0080 mm. (fig. 3), 

 the dark zone round the nucleus is seen to have increased con- 

 siderably while the light one remained stationary. The large 

 nucleus which is represented in fig. 4 shows that in some 

 cases the big nucleoli disappear almost completely, leaving an 

 unstained part around them. Frequently one spot was seen in 

 the centre of the nucleus among what is generally known as 

 the " chromatic " substance. This consists of very minute 

 granules distinguished from the rest of the nuclear substance 

 by its greater consistence, a higher refractive power, as well as 

 by its capability of assuming a strong tint in certain solutions 

 of colouring matter which are used among microscopists for 

 staining nuclei. The small granules are suspended in a net- 

 work of threads, which has so often been described in both 

 animal and vegetable cells, and which plays a conspicuous part 

 in the karyokinetic figures of the dividing nucleus. It is 



