580 
J. BBONTffc GATENBY. 
variation is quite remarkable, and no two epithelial cells 
metamorphose in quite the same way. 
In PI. 30, fig. 2, the upper nucleus has to its right a small, 
darker area in the cytoplasm, and the same applies to the 
upper part of the middle nucleus in this figure. Not all cells 
possess this cloud — or, more correctly, I should say that I 
have been unable to find the cloud in every epithelial cell. 
The cytoplasm of the germinal epithelial cell is of the open 
variety, and is best seen in preparations stained in iron alum- 
alizarin-toluidin blue, where it is a purplish-blue in shade. 
In some cases, when the cell is about to abandon its in- 
difference, the nucleus, at first a depressed oval, becomes 
spherical or semi-spherical, as shown in PI. 31, figs. 17 and 19. 
I believe that of the many variations which one finds, all fall 
roughly under three heads : In the first, one has a cell in the 
positions marked X. in Text-fig. 1, i, growing into fig. ii, X., 
in the same text-figure. Also in other cases one finds such an 
example as that of Text-fig. 2 at 1 and 2. While, again, one 
always finds cases such as that drawn in Text-fig. 3, i, X.Y., 
and Text-fig*. 4, i, and in PI. 29, fig. 1, at the roman figures (i, 
ii, iii). 
In the other cases one finds the progerminative cell as in 
Text-fig. 3, ii, S.P.P. Also it seems that these arbitrary 
classes are linked up by other classes, such as the cell 3 b in 
PI. 29, fig. 1 (explained in “ Discussion ”). 
In every case of an epithelial cell of the snail meta- 
morphosing into a germ-cell of either sex one finds two 
constant facts : one is the appearance of a fine cloud in the 
cytoplasm, which follows after the other — an enlargement of 
the nucleus. It is only by fine fixing reagents that this cloud 
is shown, but it has never before been described simply 
because the workers on the snail destroyed it with acetic acid 
or alcohol. 
I am unable to say why this cloud, which is shown in PL 31, 
figs. 11 and 19 in a very early stage, should with absolute 
constancy be found to one side of the nucleus. It may be 
that it is on the side near which lies the centrosome if tliaf be 
