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The Morphology and Physiology of the Nucleolus. 
It soon disappears, apparently through being dissolved in the 
cytoplasm. 
The function of the extruded nucleolar particles has been dis- 
cussed by me in another paper (84). Owing to the fact that 
nucleolar extrusions occur at the beginning of yolk formation and 
continue throughout this process, there is every reason for believing 
that it stands in some functional relationship to the activity of the 
cytoplasmic organs, which throughout oogenesis are engaged in 
the formation of reserved food substances for the development of 
the embryo. 
The Nucleolus during Spermatogenesis. 
The behaviour of the nucleolus during spermatogenesis has 
been described in a number of animals, and there is considerable 
uniformity in the process. I shall, therefore, restrict my descrip- 
tion to one or two features of special interest in Limndea. 
Throughout spermatogenesis the nucleolus stains oxyphil ; and 
there is no differentiation into two parts as occurs in the oocyte 
nucleus. During the early prophases of the heterotypic division 
of the spermatocyte, the nucleolus is present as a spherical plasmo- 
some held in the linin network. The disposition of the nucleolus 
during synizesis is shown in fig. 7, PI. III. At a contraction of 
the chromatin elements is just beginning; the nucleolus is seen to 
be attached to the chromatin threadwork. Later stages are shown 
at b and c. It will be noticed, that as the chromatin threads 
contract they draw the nucleolus with them. Following this 
stage with the breaking up of the chromatin elements to form the 
diplotene chromosomes, the nucleolus apparently disintegrates, 
and by the time that the double chromosomes are definitely 
formed, the nucleolus can no longer be observed in the nucleus. 
It is interesting to note here, that although the chromatin thread- 
work during synizesis stains markedly basophil, the diplotene 
chromosomes, formed from it, after the dissolution of the nucleolus 
stain amphophil with basophil preponderance. It seems possible 
that the nucleolus has some connexion with this. 
The minute size of the spermatid in Limnxa renders accurate 
observation very difficult, but so far as I have been able to see, 
there is no definite nucleolar body present at this stage, or during 
the formation of the spermatozoon. There is, however, considerable 
nucleolar activity in the sertoli or nurse- cells. 
At about the time when the tails of the spermatozoa begin to 
form, they appear to exercise considerable attraction for cells of 
the oocyte type. Some spermatids appear to group together near 
an undifferentiated cell of the germinal epithelium. Such a cell 
then seems to grow larger, and there is actual attachment between 
