178 MONTGOMERY A STUDY OF THE CHROMOSOMES 



large volume, are those designated by the letter k in Figs. 119-123; these two are of 

 approximately equal volume, and each has about half the volume of the chromosome x. 



There are accordingly present in the spermatogonic monaster thirteen chromatin 

 elements, of which two (probably the smallest) represent the chromatin nucleoli ; of the 

 eleven chromosomes, three are much larger than the others, namely, the one marked x 

 and the two marked k in the Figs. 119-123. In the metakinesis all these elements are 

 halved longitudinally. 



In the following synapsis stage we find a small chromatin nucleolus composed of two 

 parts, which in every way is comparable to the bivalent chromatin nucleolus of the growth 

 period of other Coreidce ; this is marked N. 2 in Figs. 124, 129, 130. This chromatin 

 nucleolus is peripheral in position, and only occasionally has a true nucleolus apposed to 

 it (Fig. 130). Generally its two univalent halves are not closely apposed but more or 

 less separated, often widely separated (N. 2, Fig. 131), but the two always come close 

 together to form a dumbbell-shaped, bivalent body before the monaster stage of the first 

 maturation division. Certainly its two components must represent the two univalent 

 chromatin nucleoli of the rest stage of the spermatogonia (N. 2, Fig. 118). 



During the synapsis stage also ten out of the eleven chromosomes derived from the 

 spermatogonium combine to form five bivalent chromosomes, as will be shown in treating 

 of the maturation divisions. The odd one of the eleven chromosomes does not combine 

 with any other during the synapsis stage, and this is the largest of the chromosomes of 

 the spermatogonium, namely, the chromosome x. This element has a remarkable history 

 in the growth period. Through the whole growth period it acts like a chromatin nucle- 

 olus in preserving a compact form and in continuing to take the safframne stain with the 

 use of the double stain of Hermann, while the other chromosomes take the violet stain. 

 It will be remembered that this chromosome x becomes distinguishable first in the sperma- 

 togonic mitoses (Figs. 119-123), while in the preceding spermatogonic rest stage it 

 cannot be distinguished, for then it takes the violet stain like the other chromosomes and 

 takes part in the formation of the nuclear riticulum just as they do ; accordingly it can 

 be concluded that it commences to behave differently from the other chromosomes at the 

 beginning of the growth period of the spermatocyte. In the early synapsis (Fig. 124) 

 it has the same general shape as in the spermatogonic monaster stage (compare the ele- 

 ment marked x in Fig. 124 with the corresponding one in Figs. 120, 121), but it has 

 greatly increased in volume, as a comparison of these figures show, since it will be recalled 

 that the chromosome x of the spermatccytes is a half of the chromosome x of the sperma- 

 togonia. Later in the growth period the chromosome x elongates into the form of a bent 

 rod (Figs. 125130), which usually lies close to the nuclear membrane (in this point 

 also resembling a chromatin nucleolus); throughout the growth period it keeps its com- 



