476 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
entiated assume a refractive appearance and form a center to which 
others congregate. Still other myxamoebae which pile on top, also 
become vacuolated and take up the water which the surrounding 
ones are constantly losing. An axial vertical column is thus differ¬ 
entiated in the center of the rising mass, w’hich is ultimately to form 
the support up which the colony climbs. As,more water is absorbed, 
the vacuoles gradually grow larger; in those cells in which there 
are several, they usually fuse into one, and the protoplasm of the 
individual becomes stretched until the cell is several times the 
diameter of the surrounding unvacuolated myxamoebae. These 
enlarging cells become firmly pressed together, so that the inter¬ 
cellular spaces between them are obliterated. Brefeld asserts that 
no intercellular spaces occur. It may readily be seen, however, 
when a pseudoplasmodium is examined in a drop of water, that 
young stages, or occasionally even old ones, show such spaces (pi. 
8, fig. 110). As the cells of the forming stalk take on a polygonal 
form, each secretes a cellulose wall which becomes firmly cemented 
to the walls of contiguous cells. The cells still retain a certain 
degree of individuality, however, as may be proved by the use of 
maceration agents; by this means, the cementing substance of even 
an old stalk may be dissolved, thus causing the cells to separate. 
Occasionally very favorable conditions occur in drop cultures for 
examining the development of the stalk with highest powers, as when 
a small pseudoplasmodium falls over against the cover glass. In 
such a condition, the growth of the vacuoles and the formation of 
cellulose walls may be readily observed. Stalk formation may be 
traced even more satisfactorily, however, simply by examining 
pseudoplasmodia of various degrees of development in a drop of 
water, supplemented by tests with vaiious reagents. In water, after 
pressure is applied to the cover, the middle column of the stalk 
cells of the pseudoplasmodium may be readily seen, while after 
the protoplasm has been coagulated by means of killing reagents, 
some pressure must be applied in order to disclose the forming 
axis. 
If a cover glass be pressed upon a fresh colony in a drop of water, 
it will be observed that stalk formation is proceeding in the apical 
papilla usually noticeable at the summit of all young pseudoplasmodia 
(pi. 7, fig. 96-103). It will be seen that the apical protuberance 
just mentioned is formed by a number of rapidly expanding vacuo- 
