5 
Capillitium in Certain Myxomycetes. 
at least intended to refer to something much more minute and more evenly 
distributed than these relatively large and conspicuously differentiated 
bodies. 
The most striking and perhaps the most characteristic feature in the 
whole process of the formation of the capillitium are the fibrillar asters 
which appear about the capillitial vacuoles. They consist of delicate 
fibrillar strands, extending from the forming capillitium in all directions 
through the surrounding cytoplasm. These strands are quite sharp, clean- 
cut filaments which under low magnifications seem in general to extend 
radially outwards from the forming capillitial tube. Closer observation 
shows, however, that they are really oriented on the above-mentioned 
granules (PL I, Figs. 1-4). When these granules are distributed evenly on the 
walls of the tube, the fibrils appear most nearly radial with reference to 
the forming thread (Fig. 2). Cases are found, however, in which one or 
several fibres are centred on a granule at some distance from the tube 
(Fig. 1). It is such cases as these, probably, which led Kranzlin (28) to 
regard these radial systems as actual astrospheres about genuine centro- 
somes. As a matter of fact the fibres are quite commonly not oriented on 
the centre of the capillitial thread. In many cases their course is almost or 
quite tangential to the surface of the capillitial tube (Figs. 3 and 4). This is 
due, as noted, to the fact that they are really oriented on the granules. 
A granule on the surface of the capillitial tube may be the centre for rays 
that run in several directions from it, only one of which is radial to 
the tube. 
We have not seen cases in which the rays form a complete aster running 
in all directions from a granule, nor cases in which they are oriented on 
a granule lying at the centre of the cross-section of a capillitial thread such 
as are represented by Kranzlin ( 28 ) (Figs. 14-16, Taf. IV, and Text-fig. VII, 4). 
In our material the capillitial thread in cross-section is a clear circular 
vacuolar cavity. It may and generally does contain granular material, but 
this regularly lies free in a clear unstained vacuolar cavity. The threads 
never extend through the membrane of the capillitial thread, and the latter 
is at these stages clean-cut and circular. 
In longitudinal sections the orientation of the fibrils with reference 
to the thread is shown with especial clearness. It is very evident here that 
they are centred on the granules instead of on the general outline of the 
capillitial thread (Fig. 2). They appear as irregularly distributed groups 
along the sides of the capillitial thread, a group of fibres for each granule. 
In general form they suggest the cytoasters figured by Mead and Morgan 
(36, 37) as the results of treatment with salt solutions in the cytoplasm 
of Echinoderm and other eggs. With low magnifications the cross-sections 
of the capillitial threads at these stages suggest strongly the appearance of 
astrospheres as conceived by Strasburger (43). The circular section of the 
