The Morphology and Physiology of the Nucleolus. 129 
section and produce a type of artifact which is apt to be confused 
with chromidia. An instance of such confusion is the basophil 
cloud which Gatenby described at certain stages as occurring at 
the side of the nucleus of the young oocytes of the frog. Later, 
Gatenby applied the modern technique for the cytoplasmic organs 
to investigate the nature of the “ chromatin -like” mass apparently 
issuing from the nucleus. He found it to be mitochondria. 
Probably there was an extrusion of some liquid from the nucleus 
into the cytoplasm, which stimulated the mitochondrial complex 
of the young oocyte into activity, but the extruded substance was 
not chromatin granules. 
In considering the role of the nucleolus during gametogenesis 
and embryogeny, it is desirable therefore to consider the part 
played by the cytoplasmic organs. This has been fully described 
by Gatenby in the case of Limnsea stagnalis (11). 
The young oocyte contains Golgi elements or dictyosomes 
arranged concentrically around the archoplasm, and mitochondria 
surrounding it in the form of a cloud. The behaviour of these 
two organs during oogenesis appears to be essentially similar to 
that of Patella previously described by me — i.e. the Golgi elements 
increase in number by fission and spread out in the cytoplasm, 
and while so doing lead to the formation of yolk bodies. The 
mitochondria merely divide and scatter more or less evenly 
throughout the cell ; they appear to become somewhat enlarged, 
probably with reserve food substance. At maturation, the egg 
contains yolk bodies, unchanged Golgi elements and mitochondria 
dispersed irregularly in the cell. 
During spermatogenesis, the Golgi apparatus and mitochondria 
persist in the cell until the spermatid stage is reached, then during 
the formation of the tail, the Golgi apparatus is apparently 
sloughed off, and the mitochondria undergo a chemical change and 
form a kind of sheath around the axial filament. 
During segmentation of the ovum, both Golgi apparatus and 
mitochondria persist irregularly scattered in the cytoplasm. 
Neither disappears during organogeny. In figs. 14, 16, PI. IY, is 
shown the appearance of these organs in osmic acid preparations 
during the early segmentation and blastula stages. The cyto- 
plasmic organs have been drawn to scale from the figures given 
in the paper previously referred to (11). Professor Gatenby has also 
allowed me to examine some of his preparations showing the same. 
In the present research no fixatives containing osmic acid have 
been used, but only those whose constituents are known to destroy 
and remove all traces of the cytoplasmic organs. 
Behaviour of the Nucleolus during Oogenesis. 
The behaviour of the nucleolus during oogenesis is essentially 
similar to that previously described by me in the Mollusc Patella 
K 
