178 



MONTGOMERY — A STUDY OF THE OHKOMOSOMES 



large volume, are those designated by the letter h 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 W. 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 tw ivalent 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. 1 IS). 



During I lie 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 ol 

 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 saffranine stain with the 

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

 It will be remembered that this chromosome:/: 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 lakes the violet, stain like the oilier chromosomes and 

 fakes part in the formation of the unclear rilicnlnin 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. L24) 

 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. L20, L21), 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 spermatocytes is a half of the chromosome x of the sperma- 

 togonia. Later in the growth period the chromosome X elongates into (he form of a, bent, 

 rod (Figs. L25-130), which usually lies close to the nuclear membrane (in this point, 

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



