KARYOKINESIS. 9 



size and for this reason their number cannot readily be determined since they 

 grade down to the smaller granules, which are innumerable (Plate. I, figs. 3 and 4). 

 These larger granules continually increase in size and become the chromosomes of 

 the first maturation spindle ; some of these granules stain less deeply at the center 

 than at the periphery. As the chromosomes grow in size the remaining chromatin 

 granules, which constitute the chief bulk of chromatin within the germinal vesicle, 

 grow smaller and smaller and are gradually dissolved ; on the disappearance of the 

 nuclear membrane they escape with the nuclear sap into the cytoplasm, figs. 5, 6 

 and 7. At the same time the linin threads, which were plainly visible at an earlier 

 stage, fig. 4, are no longer to be seen, but the arrangement of some of the granules 

 in radiating lines, fig. 5, is probably to be taken as evidence that some of these 

 threads still exist. In the early stages of the first maturation division, all the 

 chromatin granules stain alike, in later stages the chromosomes stain more densely 

 with nuclear stains, while the remaining granules show an increasing affinity for 

 plasma stains. In such stages as are shown in figs. 3 and 4, there are no perceptible 

 differences, save size only, between the granules which become chromosomes and 

 those which dissolve ; the fact, however, that the history of these two groups is so. 

 different shows there is some fundamental difference between them. It is highly 

 probable that the faintly staining granules which are ultimately dissolved or trans- 

 formed into linin are identical with the lanthanin or oxychromatin of Heidenhain 

 ('94). 1 



(b). Nuclear Sap. Before the solution of the oxychromatin granules and 

 nucleolus begins, the nuclear sap is a clear and almost non-colorable fluid. As the 

 solution of these elements progresses the nuclear sap becomes granular and tingible, 

 staining blue or purple with Delafield's hematoxylin alone, though it stains deeply 

 with plasma stains, such as eosin or orange G. when these are used after the hasma- 

 toxylin. Even after the nuclear membrane has entirely disappeared the nuclear sap 

 and oxychromatin can still be recognized as a granular mass, figs. 5, 6, 7. 



Korschelt ('95) has observed a similar increase in the staining properties of the 

 nuclear sap of Ophryotrocha, where the "Kernsaft" stains more and more deeply 

 as division advances until it becomes so dark that the chromatin threads are invisi- 

 ble. Then the sap loses some of its staining qualities and, at the same time, dis- 

 dissolved nucleolar substance is probably added to the chromatin threads. 



1 The term Achromatin, as used and defined by Flemming ('82, p. 375), is limited to " that formed 

 substratum of nuclear structures, as well as of the division figures, which is not colored by nuclear stains." 

 As thus defined, it is applicable only to the linin, and is not even applicable to it at all stages in the cell 

 cycle, since the linin also is colored by nuclear stains at certain stages. Furthermore, it is extremely 

 probable that oxychromatin is transformed into linin at certain stages, and that oxychromatin and 

 perhaps linin are sometimes dissolved in the nuclear sap. This interrelation of these various parts of 

 the nuclear substance makes it impossible to apply the terms "chromatin" and "achromatin" as used by 

 Flemming. Nevertheless, it is convenient to have a term which will include all of the nuclear constit- 

 uents which do not form chromosomes, as contrasted with that which does. Since the term achromatin 

 has frequently been used in this sense, and since I am unwilling to further cumber cytological nomen- 

 clature with new names, I shall employ the term "achromatin," or "achromatic substance of the nucleus" 

 to include all the contents of the nucleus except the chromatin, and even that portion of the chromatin 

 which does not form chromosomes. As thus used it includes linin, oxychromatin, nuclear membrane 

 and nuclear sap. 



2 JOUEN. A. X. S. PHILA., VOL. XII. 



