360 IsTaoliitle Yatsu. 



the history of the chromosomes agrees in the main with what has 

 been described by Griffin in the egg of Thalassema ('99). 



In passing it might be mentioned that the plasmosomes occur 

 only in the germinal vesicle, chromatic nucleoli alone being present 

 in the other nuclei. Both in the segmentation nucleus and those 

 of the blastomeres the chromosomes arise as fine threads irregularly 

 curved and sometimes attenuated towards the ends. 



^^'hat is the relation between the plasmosomes and the chromatin 

 masses in the germinal vesicle ? As I have not studied the genesis 

 of these elements I am not able to give any definite answer to this 

 question. That each chromatin mass is constantly associated with 

 a plasmosome makes us think that the relation between these cannot 

 be merely a casual one. In all probability the plasmosome gives 

 off some substance to the chromatin masses for the growth of the 

 latter. It is extremely difficult to analyze the cause of the change 

 of the staining capacity of the chromatin masses, because two 

 phenomena take place almost simultaneously; namely, the disap- 

 pearance of the smaller plasmosomes and the fading of the nuclear 

 membrane. It is, however, probable that the dissolution of the 

 nucleoli is in some way or other connected with the change of the 

 staining reaction of the chromosomes ; for the latter phenomenon 

 takes place only in the germinal vesicle, and not at every dissolu- 

 tion of the nuclear membrane in later stages. Although one or 

 two chromatin spherules are found in the larger plasmosome, the 

 relation of the nucleoli and chromosomes is in C. lacteus not so close 

 as in the egg of echinoderms, in which all the chromosomes in one 

 j^eriod take shelter in the nucleolus. At any rate our case does not 



failure of conjugation of a homologous pair of chromosomes at synizesis ; b, 

 persistence of idant-free chromosomes (vide infra) as late as the meta phase, 

 and c. separation of one chromosome into two. Of these the second nmy not 

 he the ex|»lanation of om- case, because of the fact that in some eggs there are 

 thirty-eight chromosomes in a daughter plate at tlu; anaphase of the first cleav- 

 age mitosis instead of thirty-six. In all probability our case may be due to the 

 third possibility, although I have no reason to exclude the first. At any rate 

 separation of one chromosome into two or more and fusion of two or more 

 chromosomes into one may have taken place in the course of phylogeny of 

 organisms. Without this assumption we cannot understand how such diversity 

 in nunilxM" of clu'omosonics in animals and ])lants has come about. 



