No. 2.] THE EGG OF BUFO LENTIGINOSUS. 305 



there are very few of these chromatin granules present ; in 

 others there are a large number which lie, for the most part, 

 in the center of the chromosome. In the latter case there are 

 fewer of the axial fibers and they appear much finer. Ruckert 

 has stated for the selachian ^g^ that the microsomes of which 

 the chromosomes are composed at an earlier period change into 

 fine fibers, so that at one time the whole chromosome appears 

 as a filamentous structure. Such a stage, if it occurs in the 

 Qgg of Bufo, will be found during the hibernation period. The 

 presence of a varying number of chromatin microsomes in 

 the midst of the axial fibers of the chromosomes in the 

 youngest eggs obtained in the spring shows that the filamen- 

 tous structure of the chromosomes is being resolved into a 

 microsome structure. At this period the chromosomes still 

 occupy the center of the germinal vesicle, although they are no 

 longer surrounded by a ring of nucleoli, as most of the latter 

 have migrated to the side of the germinal vesicle nearest the 

 periphery of the o.g'g (PI. XXVIII, Fig. 6). Owing to the dif- 

 ferent lengths of the chromosomes, to their close intertwining, 

 and to the fact that they stain very faintly at best, it has been 

 impossible to count their number accurately. In many cases 

 the chromosomes appear to be separated off in pairs ; but this 

 arrangement is by no means general until the next stage, when 

 the axial fibers have entirely disappeared and the chromosomes 

 are composed of a single series of perfectly round microsomes 

 which take a very intense carmine stain (PI. XXVIII, Fig. 8). 

 Instead of forming a compact mass at the center of the germi- 

 nal vesicle, as in the previous stages, the chromosomes now 

 become scattered over a considerable area, and all are distinctly 

 paired as described by Ruckert in the later maturation stages 

 of the selachian ^gg, by Fick in Axolotl, and by Born in 

 Triton. There is still considerable variation in the size of the 

 chromosomes, as well as in their arrangement. Some are long 

 and slender, others short and thick ; but the two chromosomes 

 forming a pair are always of the same length. Two of the 

 chromosomes may be united in the form of an X ox Y,2. single 

 or double figure eight, or they may lie parallel for part of 

 their length and the ends intertwine in various ways (Fig. 8), 



