62 CYTOLOGY 



CHAP. 



the latter case the oocytes are retained in the oviducts (waiting for the 

 previous batch of eggs to hatch) longer than in the former, and that this 

 delay accounts for the greater diffusion of the chromosomes. 



This idea that the amount of diffusion of the chromosomes is in a 

 certain degree a function of the length of time which elapses between 

 syndesis and metaphase L is supported by the observation of Matschek 

 (1910) that those Copepods in which the chromosomes undergo only a 

 moderate amount of diffusion in the germinal vesicle stage belong chiefly 

 to those species which lay comparatively few eggs at frequent intervals 

 {Cyclops gracilis, Heterocope saliens), while those in which diffusion is 

 carried to great lengths mostly lay numerous eggs at long intervals 

 {Diaptomus castor). 



(2) The Relation between the Chromosomes and the Nucleoli 



Many cytologists believe that the nucleoli of the germinal vesicle act 

 as temporary storehouses of chromatin, receiving this substance from the 

 chromosomes at the beginning of the growth period, and giving it back 

 to them at the end of it. This conclusion is based on the facts (i) that 

 in the beginning of the germinal vesicle stage the staining capacity of 

 the chromosomes diminishes, while the size and number of the densely 

 staining nucleoli increase ; and (2) that at the end of this stage the 

 chromosomes regain their chromatic character, while the nucleoli break 

 up or give other evidences of degeneration — such as the development 

 of vacuoles. 



Many other cytologists, however, deny any such direct relationship 

 between the nucleoli and the chromatin, and this is the view which 

 appears to be best supported by recent researches (for example, 

 Jorgensen's comparative study of the nucleoli of the germinal vesicles 

 of a large number of animals, 1913). 



In any case, only very Uttle of the nucleolar mass in the germinal 

 vesicle could contribute to the formation of the chromosomes, since 

 these in their final form are, in combined bulk, very much smaller than 

 the nucleolar mass (Fig. 26). The residue of this substance is thrown 

 out into the cytoplasm when the nuclear membrane is dissolved in 

 prophase L, and there degenerates. 



In the descriptions of somatic mitoses and of spermatogenesis we 

 have generally avoided the use of the term " nucleolus," substituting 

 either " plasmosome " or " karyosome " as the case might be. The 

 germinal vesicle nucleoli do not appear to come under either of these 

 headings. Their chromatin staining reaction shows that they are not 

 merely plasmosomes, while on the other hand their relations — or rather, 

 lack of relations — to the chromatin structures of the nucleus prevent 

 one from calling them karyosomes. In many cases they are of a double 



