358 ADOLPH R. RINGOEN 
long. At this stage the constituent cells of a gland rudiment, 
and as illustrated in figure 3, have simply elongated and are 
pushing their way out into the underlying mesodermic tissue. 
During the pushing and burrowing of an outgrowth down into 
the mesodermic tissue there is an actual migration of its cells. 
Now the nuclei have increased greatly in size, as compared with 
those shown in the gland rudiment of figure 3, and at this stage 
they tend to occupy the most distal parts of the outgrowth. - 
No doubt the increase in the size of the nuclei at this time— 
preparatory to division—is associated with the fact that the 
cells which contain them are to grow out still further at a sub- 
sequent time, and obviously this requires additional cells (see 
fig. 5, also from a specimen 137 mm. long, for documentary 
evidence on the further growth of a gland rudiment; increase 
in the number of nuclei with a distinct change in their size and 
shape, as compared with fig. 4). Cell outlines are just as dis- 
tinct here as they were before the gland rudiment cells began 
to grow out into the mesodermic tissue (compare ftg. 2 with fig. 3). 
In slightly more advanced stages of differentiation than is 
represented in figure 4, an outgrowth becomes more or less 
tubular inform. This condition is represented in figure 5, also 
from a 137-mm. specimen. With still further differentia- 
tion, as I shall attempt to show at a subsequent time, this simple 
condition is radically changed. 
Another point of considerable interest in connection with 
figure 5 is the position of the nuclei in the tubular outgrowth. 
Those located in the region where the gland rudiment first 
burrowed do not seem to present any definite arrangement 
in their distribution within the outgrowth. On the other hand, 
most of the nuclei which are found in the lower half of the out- 
growth show that their long axes are placed parallel to the long 
axes of the tube. In slightly more differentiated outgrowths 
this parallel arrangement is decidely modified. Even as shown 
in figure 5, there is a slight tendency in this direction, for 
several of the nuclei are on the verge of shifting their axes.’ 
2 The nuclei, as will be pointed out later, are not actually changing their 
long axes, but the cells containing them are shifting. 
