4 Harper and Dodge. — The Formation of the 
ordinary tonoplastic boundaries enclosing non-stainable sap like that in 
ordinary vacuoles. In section the arrangement and relations of the vacuoles 
suggest somewhat vaguely that of the cleavage vacuoles in the sporanges 
of Pilobolus or Rhizopus . In reality, however, their relations are quite 
different. The cleavage vacuoles become connected by extended knife-edge 
cleavage furrows, while these capillitial vacuoles anastomose, as noted by 
tubular extensions, which soon come to have the constant diameter of the 
future thread. The pathway of the threads through the cytoplasm and 
their cavities may be said to be already determined at this stage. The 
series of connected vacuoles form in fact an extremely nodular thread, the 
vacuoles constituting a series of vesicular expansions on a continuous 
vacuolar opening whose course through the cytoplasm is roughly that of 
the future thread (Fig. n). At this stage the system of anastomosing 
vacuoles may be compared in its form to the mature capillitium of Physarum , 
Badhamia , and Tilmadoche , and the evidence is strong that the latter 
represent a more primitive stage through which the capillitium of Trichia 
and Hemiarcyria passes in its development. The stages immediately 
following involve what may be characterized as the smoothing up of this 
series of vesicular expansions into the tubular capillitial thread of practically 
constant diameter throughout its whole extent. All stages in this process 
of equalizing the diameter of the capillitial tube can be found in great 
abundance. It consists for the main part apparently in the reduction of 
the transverse diameter of the vesicles with a corresponding increase in 
their length. This lengthening of the vacuoles in the axis of their con- 
necting anastomoses and the consequent increase of the total length of the 
series lead thus to the still more tortuous windings of the ripe capillitial 
threads. The narrow connexions of the original vacuoles soon reach the 
size of the capillitial thread, and the greater part of the change in form of 
the original series of vacuoles seems to go directly to increase their length 
by reducing their transverse diameters. The capillitial thread is nodular 
and uneven in diameter for a considerable period, as is shown in Figs. 8, 9, 
10, and 11. As it gains its permanent form as a contorted tubular opening 
through the cytoplasm, its membrane becomes more distinctly differentiated 
as the wall of the future capillitial thread. From an early stage deeply 
staining granules of various forms are abundant in the region of the vacuoles 
(Fig. 1). They are especially abundant in Hemiarcyria . They may be on 
the surface of the thread or some distance from it, and may be single or 
in groups or series (Figs. 1-4). They tend to take the safranin stain 
quite characteristically. It is possible that the process of fixation disturbs 
the position of these granules, and that normally they all lie directly on the 
wall of the capillitial thread. These granules should perhaps be identified 
with those described by Strasburger, but it seems more probable that the 
idea of membranogenous corpuscles, on which he lays such emphasis, was 
