6 
Harper and Dodge . — The Formation of the 
capillitial thread represents the centrosphere, and there are frequently 
granules in the cavity of the thread which may represent one or several 
centrosomes. These granules are, however, rarely so placed in the centre 
of the thread section as to really represent a centrosome or microcentrum. 
With low powers, however, the fact that the radiating fibrils are centred on 
granules on the walls of the capillitial thread rather than on the general 
outline of the thread itself is not conspicuous, and the superficial resemblance 
of the whole structure to the polar view of a karyokinetic figure is very 
striking. 
The fibres of one system may extend through the cytoplasm until they 
reach and mingle with those from the next adjacent system (Fig. i). In 
the region outside the nuclear zone the fibres are less numerous, but those 
which do extend so far are generally quite thick and conspicuous. They 
may even appear to taper and thin out as they pass into the denser cyto- 
plasm inside the nuclear zone. The direction of the fibres is apparently not 
influenced in any way by the nuclei. They run past and among the nuclei 
without showing any evidence of connexion with or origin from them. The 
nuclei show no conspicuous centrosomes at this stage, and there is no possi- 
bility of confusing the appearance of the capillitial asters at this stage with 
any such phenomenon as { heteropolar nuclear division 5 or anything of that 
sort. In the triple stain the fibrils perhaps tend slightly to take a violet 
colour. As noted, the fibres, centred on granules as they are, may run quite 
tangentially to the surface of the capillitial thread. Sometimes these 
tangential fibres all diverge from the radial in the same direction and produce 
an appearance as if the capillitial thread had twisted on its long axis. The 
differentiation of the membrane of the capillitial thread goes on rapidly 
during this period, while the radiating fibrils are conspicuous and the nuclei 
maintain their zonal distribution. 
The conditions suggest rather strongly that the fibrils represent cyto- 
plasmic streams which are bringing in material for the formation of the 
capillitial wall and its thickenings. It would seem in this case that the 
above-mentioned granules on which the rays are centred ought to be distri- 
buted quite regularly on the boundary of the forming capillitial thread. 
This, however, is not the case, and the granules cannot be regarded as at all 
fully representing the material brought in, even in case the fibrils are 
interpreted as having their origin as streams of cytoplasm. 
The nuclei maintain their peculiar zonal distribution about the capillitial 
threads until the spiral thickenings of the latter are well outlined. The 
spirals when first formed are markedly granular. They plainly constitute 
thickenings formed on the membrane of the capillitial tube, which is faintly 
recognizable before they make their appearance. Stages can be found 
when the spirals are mere rows of granules seen only with the greatest 
difficulty and under the most favourable optical conditions. They seem to 
