35 
in the Root- Apex of Phaseolus. 
chromosomes are definitely derived from the nucleoli. The young nucleus 
contains a much convoluted, apparently continuous thread. A portion of 
this becomes transformed into nucleoli (primary nucleoli). The remainder 
becomes resolved into granules, some of which dissolve, and the others are 
converted into secondary nucleoli. The nucleus now contains only nucleo- 
plasm and primary and secondary nucleoli. Both primary and secondary 
nucleoli become resolved into filaments which present very complicated 
figures. They are ephemeral, however, and again break up into granules, 
some of which contribute to the formation of new secondary nucleoli. 
These again produce new filamentous figures which are also ephemeral and 
from which comes a third generation of secondary nucleoli, and so on for 
a number of generations. All the filamentous figures found in the nucleus 
up to the time of the first polar kinesis have thus a nucleolar origin, and 
finally a portion of the products of this nucleolar resolution is dedicated to 
the formation of the nuclein elements (chromosomes) of the first maturation- 
spindle. 
Montgomery 1 comes to the following conclusions concerning the 
structure and function of the nucleolus. 
The ground-substance of the nucleolus is more or less dense, homo- 
geneous, or granular, and either fluid or viscid in consistency. In Spirogyra 
it has a true membrane. Vacuoles are normal structures. The alveolar 
structure of nucleoli described by various observers (e.g. Cavara) is probably 
referable to the regular distribution of equal-sized vacuoles in the nucleolus. 
Nucleolini, granules within the nucleolus, have frequently been observed, but 
no particular morphological significance can be attached to them. They 
appear to be only detached portions of the nucleolar substance, and may in 
some cases be only small vacuoles. 
Two kinds of nucleolus may be seen in some animal egg-cells, the 
nucleolus proper and the paranucleolus or Nebennucleolus. The para- 
nucleolus usually stains less deeply with nucleolar stains. It is probably 
not present in plant-cells. Some observers consider the paranucleoli to 
be derivatives of the nucleolus. Hacker regards them as secretions 
of the chromatin. Montgomery considers that they may represent those 
portions of the nucleolar substance which are deposited last, after the nucleus 
has undergone important physiological and chemical changes, the first 
portion produced being the nucleolus proper. In some cases a double 
nucleolus is found, the component parts of which may each represent 
a true nucleolus ; or such a double nucleolus may consist of a true nucleolus 
in apposition to a chromatin-nucleolus. The chromatin-nucleolus may be 
a metamorphosed chromosome (in Pentatomoi) ) or, as in the larva of Carpo- 
capsa , it may originate from one of the granules of the nuclear reticulum 2 . 
1 Comparative cytological Studies, with especial regard to the Morphology of the Nucleolus,, 
Jour, of Morph., xv, 1899, p. 265. 2 Loc. cit., p. 519. 
D % 
