248 WILBUE WILLIS SWINGLE 
one-half of which sometimes migrates toward the pole of the 
spindle more quickly than does the other half to the oppo- 
site pole. The figures of Levy indicate that the body described 
by him as the sex chromosome is in all probability of the same 
nature as the precociously dividing chromosome described by 
myself. Further work on Rana temporaria will in all likelihood 
bring it into line with other species in regard to chromosomal 
constitution. 
The twenty-eight somatic chromosomes of Rana catesbeiana 
may be divided into four groups: 1) Large V- or J-shaped ele- 
ments; 2) intermediate sized J's; 3) small J's and, 4) slightly 
curved rods. These chromosomes appear to be definitely paired 
according to size and shape, and in this respect resemble those of 
other amphibians. It should be stated, however, that the chro- 
mosomes, though occurring in pairs in regard to size and shape 
relations, are not always found side by side within the nucleus. 
Many times the members of a pair are widely separated and may 
be on opposite sides of the nucleus. In general, though, the two 
homologues are usually near one another. Certainly, the inti- 
mate pairing of somatic chromosomes, such as described by Metz 
('14) for Drosophilia and by Whiting ('17) for the mosquito, does 
not occur in the Anura (figs. 4 to 6). 
The size and shape of the spermatogonial chromosomes vary 
somewhat with the fixative used, particularly if the fixation is not 
of the very best. The size variation is due to the preserving 
fluid and not to any real variation of chromosomal size or shape 
in the hving tissue. In extreme cases the chromosomes may 
appear as short blocks, and their characteristic shape is entirely 
lacking (fig. 5). It is interesting in this connection to compare 
King's ('07) figure 10, plate 1, with my figure 5. King regards 
the chromosomes figured by her as those by young spermato- 
cytes before the stage of reduction (p. 368). They look very 
much like the short dumpy chromatin blocks of my figure 5. 
This cell is an ordinary spermatogonium in prophase, in which 
the spireme segments have either been greatly condensed by 
imperfect fixation or else the cell was abnormal, probably the 
latter is the case, as such cells appear in otherwise excellently 
