3 
Capillitium in Certain Myxomycetes. 
stage we have observed threads and fibrils of considerable length irregularly 
distributed in the cytoplasm (PI. II, Fig. 6). In some radial sections of quite 
young sporanges of Hemiarcyria , these fibrils form a series running from 
the base and centre of the sporange outwards towards its periphery as if 
they marked the path of currents flowing into the sporange from the 
plasmodium below. 
As Strasburger ( 43 ) described, the formation of the capillitium begins 
with the appearance of vacuoles of oval or irregular outline, which early 
become connected together to form series and anastomosing systems of 
rather angular openings in the cytoplasm. Such stages are shown in Figs. 8, 
9, 10, it, and 12. Fig. n shows eight such connecting vacuolar openings 
which are irregularly three-cornered in outline, and are connected by more 
or less narrow tubular branches. The cytoplasm immediately surrounding 
these vacuoles becomes very dense, with many fibrils more or less radiately 
arranged. The nuclei, as noted, are at first rather evenly distributed 
through the cytoplasm, but simultaneously with the appearance of the 
vacuoles they begin to take up a characteristic position which persists 
through the whole process of the differentiation of the capillitial threads. 
They at first move away from the vacuoles to a rather constant distance, 
equal to about three or four times their diameter and just at the surface of 
the denser layer of cytoplasm. For a time their distribution further out in 
the intervacuolar spaces seems to remain unchanged, especially in Hemi- 
arcyria (Figs. 13-15). Later these outer nuclei seem to migrate also, 
moving inward toward the vacuoles, so that they are all finally gathered in 
quite a definite layer around the forming capillitial threads (Figs. 16-19). 
Between this nuclear zone and the vacuoles the cytoplasm is quite dense ; 
beyond the nuclei it is much more openly reticulated in its appearance 
(Figs. 8-10). 
The nuclei have evidently gathered about the vacuoles in which the 
capillitial threads are to form, but appear also to be crowded back in some 
degree out of the denser plasm which immediately surrounds the vacuoles. 
As noted, this characteristic relation between the distribution of the nuclei 
and the position of the forming capillitial threads persists till the threads 
have attained their normal form and diameter. The vacuoles are at first 
rather angular and connected by narrow anastomosing extensions into 
series which wind tortuously through the cytoplasm in the fashion of the 
future capillitial threads (Figs. 7 and 8). If the mature capillitium is to consist 
of simple unbranched threads, as in Trichia , the vacuoles form single series, 
or possibly a single vacuole may elongate to form a thread ; if the capillitium 
is to form a reticulated net the connexions of the vacuoles are formed 
accordingly, i. e. a single vacuole may become connected with three others 
instead of with two only (Figs. 9-1 1). The vacuolar membranes show 
no special thickening or differentiation at this time. They are apparently 
