270 NAOKI SUGITA 
maturity at twenty-one to twenty-five days of age. At that age 
the cells are nearly full size. We may conclude, therefore, at 
least regarding some of the nerve cells, that the beginning of 
functional education of the cells at twenty days is preceded by 
the attainment of nearly full size, and after this period there is 
very little change in size, though the internal structures mature 
as the age advances. 
Mouse. <A study in this field was made by Stefanowska (’98) 
on the cortical cells of the mouse. She stained the cells by the 
method of silver impregnation and studied mainly the develop- 
ment of the cell attachments. Her conclusions may be condensed 
as follows: 
1. In the new-born mouse most of the cortical nerve cells have a 
simple morphology. 2. The cells are usually arranged in chains, dis- 
posed perpendicularly to the surface of the cortex. 3. Besides these, 
there are some groups of cells more advanced in developmen. and 
having many dendrites, and cells which have the adult form having 
many, long, ramified dendrites. 4. The different parts of the cortex 
do not attain the same degree of development at the same time. Some 
cell groups are more precocious. 5. In the lamina multiformis and 
in the lamina ganglionaris, we find always the most advanced cells 
in large numbers. 6. In the lamina pyramidalis the development of 
the cells is very slow. On the ectal surface, near the pia mater, many 
cells not at all differentiated are often found. 7. At one day after 
birth, the dendrites of cortical cells are covered with varicosities. The 
axis-cylinders have also many nodal swellings. 8. As the neurons 
develop, the varicosities become more and more rare. At fifteen 
days, varicosities are no longer seen on the dendrites and the neurons 
at this age have completed their development. 9. The appearance 
of the piriform appendices on the dendrites is somewhat delayed. 
At ten days all pyramidal cells show these appendices. These latter 
are the constant feature of the neuron, while the varicosities are only 
a temporary formation. The piriform appendices may be the terminal 
apparatus of the dendrites. 10. The piriform appendices are the 
last element which appears on the cortical cells during growth. This 
fact seems to suggest the high importance of these appendices for this 
nerve function. 
As seen from the foregoing, the morphological completeness in 
respect of the dendrites and the axis-cylinder of the cortical cells 
is attained at fifteen days or at the weaning time of the mouse 
also. 
