206 WALTER HEAPE, 



fig. 2 was taken. I tore open these ova and isolated their 

 nuclei ; the one represented in fig. 3 was flattened by with- 

 drawing the fluid in which it was immersed from beneath the 

 coverslip, the other two are, as nearly as may be, not under the 

 influence of pressure. In all of them a homogeneous nuclear 

 substance bounds a central clear space in which lies the 

 nucleolus. Besides the nucleolus a small number of large and 

 small highly refractile irregular-shaped bodies are contained 

 •within the nucleus. 



In fig. 4 the nucleolus, which is not bounded by a membrane, 

 consists mainly of an aggregated mass of minute granules, a 

 single larger granule being embedded in the midst of these. A 

 ring of four very large irregular granules surrounds the nucleolus, 

 and a few fine granules are contained in the peripheral nuclear 

 substance. 



In fig. 5 the boundary of the nucleolus is more distinct, 

 and the transparent space surrounding it is well marked. A 

 few small and medium-sized granules are contained within the 

 nucleolus, while a number of small particles are suspended in 

 the nuclear substance. 



Fig. 3 shows still further difi'erentiation. The nucleolus is free 

 from granules, is contained within a definite sharply-marked 

 outline, and within the nucleolus itself an appearance of radial 

 striation may be noticed. A ring of large granules (broken 

 by pressure) surrounds the nucleolus, and a number of smaller 

 particles are distributed peripherally. 



It appears, therefore, from an examination of these three 

 nuclei, that a single nucleolus only is present, and that a 

 variable number of larger or smaller or of both-sized granules 

 are also contained within the nucleus. The nucleolus is 

 situated in a transparent central portion of the nucleus, while 

 in the peripheral homogeneous nuclear substance a number of 

 minute highly refractile granules are suspended. A few larger 

 irregular-shaped granules may be arranged close around, but 

 distinct from the nucleolus, while the latter may itself contain 

 smaller granules. Whether or not the isolated granules are to 

 be regarded as nucleolar material is a question I do not pretend 



