Capillitium in Certain Myxomycetes. 9 
metrically developed and oriented secretion products, the conditions here 
suggest those in the formation of the siliceous framework of the Radiolarian 
skeleton as analysed by Haecker (19) and others. It is interesting to note 
that Haecker is inclined to conclude that the formation and orientation of 
the Radiolarian endo-skeleton are controlled by so-called ‘ regulating centres’, 
which may have arisen by multiple central body formation. Such a con- 
ception is in striking agreement with Kranzlin’s (28) account of the origin 
of capillitium initials from centrosomes. As noted, however, our observa- 
tions indicate that the radial fibrillar systems about the capillitial vacuoles 
are not oriented as Kranzlin described, and do not arise as spindle-poles and 
asters. As intraprotoplasmic secretion products the capillitial threads cer- 
tainly have the closest possible analogy with the protozoan endo-skeleton, 
but the capillitium shows no such specialized orientation as is found in the 
case of the endo-skeleton. 
The appearance of figures so closely imitating the polar asters of the 
mitotic figure in connexion with a purely vegetative process of secretion, 
and in no direct connexion with the processes of nuclear or cell-division, 
affords an opportunity for the examination of their functions and the con- 
ditions involved in their formation, free from the assumptions associated 
with their activities in connexion with the movements of chromosomes, &c. 
We have referred to the evidence that these figures are due to streaming (20). 
The fact that the formation of the capillitium implies the deposition of 
materials in the vacuolar spaces first formed naturally suggests that these 
more or less radially placed lines mark the pathways by which materials 
are .brought in from the surrounding cytoplasm. The accumulation of the 
nuclei in a quite definite zone at a rather constant distance from the forming 
thread may be taken as fuither evidence of their relation to the metabolic 
factors in the growth and morphogenetic processes here involved, and 
suggests that they may in this case be concerned in some way in the pro- 
duction of the material to be used in the formation of the capillitium. 
It is clear, as we have shown, that the aggregation of the nuclei in this 
zone involves the migration of some of them towards the capillitial vacuoles, 
as well as the crowding back of others out of the dense cytoplasm imme- 
diately surrounding the vacuoles. Our preparations give no suggestion as 
to just how these nuclear movements are brought about. But that the 
nuclei do come to lie in a definite zone is a most conspicuous fact, and must 
certainly be conceived as related in some way to the formative processes 
going on in the capillitial vacuole. It is to be remembered, however, that 
the radial fibrils in many cases extend between and beyond the nuclei, and 
hence cannot merely mark lines of flow from the nuclei to the forming 
threads. 
The formation of the capillitial thread membrane with its sculpturings 
may be conceived as comparable to the ordinary processes of cell-wall 
