THE HISTOLOGY OF THE BLOOD OF LARVA OF LEPIDOSIREN PARADOXA. 299 
laterally by very distinct fibrille. These branch, and the branches join at the equator 
those of the fibres of the opposite astral system, while the outermost threads abut 
against the cell membrane, and those from opposite poles are seen to meet at the point 
where it is becoming infolded (PI. II. fig. 15 ; Pl. V. fig. 39). There is no thickening of 
the membrane at the point of infolding. 
I have shown that at all stages the axial system of fibres is very feebly developed. 
The contortion of these fibres in the anaphase cannot be due to any ‘ pushing’ force 
exerted along them, but rather I believe to the accumulation at, or determination 
of fluid to the equator of the corpuscle. In some preparations I have seen an actual 
yacuole occupying the spindle axis, as if the protoplasmic threads had been wholly 
withdrawn towards the poles. 
The subequatorial fibres become more strongly marked at this stage, and it is 
certainly suggested that the lines of force are now directed on the cell periphery, and 
the picture gives the idea that the force that is exerted by or along the lines of these 
threads is rather a tractive than a pushing one. The determination of fluid to the 
equator seems coincident with the passage of the chromosomes to the spindle poles. 
It is to be noticed that the distance between the spindle poles is distinctly increased at 
this stage. 
Stages intermediate between that represented in PI. II. fig. 15 and that shown in 
fig. 17 are rare, suggesting that once the infolding is produced, the cell division is 
quickly completed. 
The subequatorial threads, still attached to the cell membrane at the bottom of the 
furrow, come to be stretched in a straight line between the spindle poles (PI. V. fig. 40), 
and at a later stage (PI. II. fig. 16; Pl V. fig. 41) form, with the loose fibres in the axis 
of the spindle, an hourglass-shaped system of fibrillze. These are grouped apparently in 
bundles, which contract into the ‘mid-body’ when division is complete. This has not 
the ring form seen in some cells, but is a large single body, probably formed from the 
smaller single granules on the bundles of threads of the previous stage (Pl. II. fig. 17). 
Tt becomes drawn out into a longish thread when the daughter corpuscles separate from 
one another (Pl. II. fig. 18; Pl. V. fig. 43). 
The centrosome undergoes little merease in size during mitosis. There are no 
phenomena comparable to the enlargement of the sphere which occurs in dividing ova. 
In the late anaphases it is drawn out somewhat tangentially, and in the telophases it 
begins to dwindle. It lies in the hollow of the reconstructing nucleus and is difficult to 
detect, but in oblique sections it is seen standing out clear of the nucleus; and in such 
sections, although I have given much attention to the point, I have not been able to 
convince myself that it was in any case duplicated (cf fig. 17, Pl. IL). 
In fig. 18, Pl. Il. an appearance suggestive of a division is drawn, but careful 
examination proved that the radiations were all focussed on one point, and that the 
appearance was an accidental one, due probably to defective fixation. Similar deforma- 
tions of the reticulum are met with in other cells removed from the centrosomal area. 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART II. (NO. 11). 45 
