The maturation and fertilization of the egg of Cerebratulus. 435 



that these structures are not of the same general nature, for, as we 

 shall see below, the staining properties of certain parts of the cell 

 are greatly altered by very slight changes in their chemical com- 

 position. 



The chromatic network of the nucleus undergoes a rapid change 

 at the time the egg is laid. Instead of the deeply staining, more 

 or less regular network of chromatin seen in the ovarian egg, we 

 find that nearly the whole network loses its power of holding the 

 haematoxylin, and consequently is stained in good preparations only 

 by the so-called plasma-stains. A the same time a considerable 

 number of small granules are found which retain their affinity for 

 haematoxylin, and even acquire a capacity for a much deeper stain. 

 These granules gradually coalesce to form larger, spherical or irregular 

 bodies (Fig. 1) which, by their further fusion, form about sixteen 

 apparently ring-shaped chromosomes '). These are found later in the 

 first polar spindle. In the intermediate stages, when the chromatin 

 granules have united into perhaps thirty or forty larger bodies, these 

 are found to lie in little groups of about six to twelve each. As 

 the fusion proceeds further these groups collect themselves towards 

 that portion of the germinal vesicle which lies nearest the outer 

 boundary of the egg ; that is, on that side where the first polar spindle 

 is to be found. This migration takes place often while the nuclear 

 membrance is still intact, so that it is difficult to understand by what 

 mechanical means it is accomplished. The irregularly ring-shaped 

 chromosomes resulting from the fusion of the chromatic particles, 

 mentioned above, are about sixteen in number-), and measure not 

 far from 0,002 mm in diameter. Of the whole amount of chromatin 

 present in the egg before laying, only the minute quantity contained 

 in these small bodies retains its chromatic character. All the rest 

 degenerates and is gradually absorbed by the cytoplasm. 



After the asters of the first polar spindle have appeared and the 

 nuclear membrane has been dissolved away in places, this former 



1) These chromosomes often occur in the form of nearly complete 

 hollow spheres, or of hollow spheres which have had the polar regions 

 removed. 



2) The exact number is difficult to determine with accuracy, not 

 only because two portions of a single chromosome are often found in 

 two different sections, but also on account of the fact that two or more 

 chromosomes may lie so close together that the boundaries of the in- 

 dividual chromosomes are indistinguishable. 



