May, 1909.] Nuclear- Divisions in Convallaria 499 



the wall (Fig. 6) . The chromatin granules are now quite uniform 

 in size and shape, and the spireme exists as a single thread 

 throughout its entire length (Figs. 6, 6b). 



After synapsis a loosening or unwinding of the thread begins. 

 The linin becomes thicker, the granules elongate, and the 

 spireme becomes shorter, although it again occupies the whole of 

 the nuclear cavity (Fig. 7). Then an apparent division of the 

 granules takes place and a double row can be seen (Fig. 8a). 

 Occasionally a part of the thread appears still single while the 

 rest is double (Fig. 8a). This appearance would be the same if 

 the granules were dividing or conjugating. The fact that the 

 granules lying opposite each other are so much alike in size and 

 shape is all that makes this appear to be a division of the thread. 

 There is quite a marked decrease in chromatin matter, however, 

 and this, at first sight, would favor a conjugation, but it must be 

 remembered that the spireme is rapidly contracting (Figs. 7, 8, 

 9). After a short time this doubleness is no longer apparent. 

 For the present this will be considered a temporary division of 

 chromatin granules. In later studies the author intends to give 

 this step more consideration. 



With continued thickening the ribbon begins to show an 

 arrangement into definite loops (Figs. 9, 10, 11), which later 

 become sixteen chromosomes. Just how these are formed from 

 the thirty-two of the spermatogonia has not yet been determined. 

 They are of various shapes and sizes, but a common thickness. 

 In fact, thickness seems to be the only factor which the sixteen 

 chromosomes have in common. They are apparently twice as 

 thick as the chromosomes of the sporophyte cell. Since the 

 relative stage of development of chromosomes was found to gov- 

 ern thickness, it was thought advisable to compare for this pur- 

 pose chromosomes of nearly the same stage. Figs. 17, 21, 26, 

 show telophases of cells after the first reduction division, second 

 reduction division, and sporophyte cell division, respectively. 

 The fact that the daughter chromosomes of Fig. 17 are so much 

 thicker than those of Fig. 26 seems to indicate that the phe- 

 nomenon after synapsis might have been a pairing of granules. 



There is, usually, one chromosome which is much longer than 

 the others. In Fig. 13, it is the fourteenth chromosome. It 

 shows a lobing at one end. Many of the chromosomes at this 

 stage show a lobing at either, or both ends. (Fig. 12a). This 

 lobing is either the beginning of the longitudinal division, or else 

 it is a remnant of the double phenomenon noticed shortly after 

 synapsis. The nucleolus now fragments and passes into the 

 cytoplasm. With the ejection of the micronuclei radiations in 

 the cytoplasm appear, and with their polarization the chromo- 

 somes assume a median position between the two centers of 

 radiation. No centrosomes are present. This is the prophase 

 of the first reduction division. Fig. 14 is a very late prophase or 

 early metaphase. 



