204 
Katharine Foot and E. C. Strobell 
form, while the surrounding chromatin becomes differentiated into a 
reticidum. 
Stages of the differentiation of the reticidum are seen in plate XVII, 
photos 45 — 54, and further demonstration of these stages is given in 
plate XVI, photos 26 and 27 and photos 29, 33 and 34. Tliat the ehromo- 
somes arise from this reticidum is shown in plate XVI, photos 27, 29, 33, 
34 and 35, also in plate XVI, photos 52 — 55. The largest two chromosomes 
of the female group of fourteen are, as a ride. derived from the nucleolus 
though we have some preparations in which all the chromosomes appear 
to arise from a reticidum or spireme, but in such cases no chromatin 
nucleolus is present. 
The differentiation of a part of the chromatin into a nucleolus which 
later gives rise to the two large cliromosomes, is a factor tliat aids us in 
determining tliat the contents of the large nuclei of zone B may frequently 
become differentiated into a number of smaller nuclei without any evidence 
of mitosis, for it can be shown that part of the chromatin of these large 
nuclei segregates into a number of nucleoli and that from eacli of these 
nucleoh may arise the two large chromosomes of the female group. The 
facts indicate that at least part of the chromatin of the nucleolus contri- 
butes to the formation of the two large chromosomes, for the transitional 
stages in the differentiation of the chromatin of the nucleolus into these 
cliromosomes can be found, and it is an interesting fact that the forms 
assumed during these stages closely resemble the forms assumed by the 
chromatin nucleolus of the spermatocytes. 
The nucleolus of photo 26, plate XVI is a single typical nucleolus. 
In photo 27 such a nucleolus is evidentlv breaking down and contributing 
to the chromatin threads. In the largest nucleus of photo 29, a nucleolus 
is again seen to be breaking down and forming part of the chromatin 
spireme. In the larger nucleus of photo 30 the chromatin nucleolus has 
evidently given rise to the two dense chromosomes, and photos 31 and 32 
show what appears to be earlier stages of the same process. In photo 33 
the chromatin nucleolus has evidently given rise to the single long dense 
chromatin thread which is probably a propliase of the two large chromo- 
somes. These conditions are further demonstrated in plate XVII, eacli 
of the three nuclei of photo 44 has quite a typical nucleolus, and the same 
relation existing between nucleus and nucleolus is shown in photos 45 — 47. 
The variability in form which is characteristic of nucleoli in general is 
shown in many of the photos. In photo 46 one of the nuclei has a double 
nucleolus and in one of the nuclei of photo 53 there are two nucleoh 
nearly equal in size. Again in one of the nuclei of photo 47 there are 
