508 Farmer . — On Spore- Formation and 
nucleus is determined proximately at least by the cell-proto- 
plasm ; and that if circumstances admit of it, the original 
four separate strains are replaced by two , which act in the 
direction of the resultant. It may further be observed that 
a closer similarity exists between these quadripolar spindles, 
and ordinary bipolar ones, than might at first sight appear to 
be the case. It is usual for a cell to divide transversely to 
its own long axis, and it is a significant fact that the nucleus 
is acted upon by a larger mass of protoplasm in this than in 
any other direction. It is known that the order of succession 
of walls in spherical cells may sometimes vary, and it may 
well be that slight differences in the general symmetry of the 
whole cell determine ultimately the particular axis of such 
nuclear divisions ; thus the geometrical considerations, so 
clearly enunciated by Sachs, harmonize also with the dyna- 
mics of cell-division as deduced from a study of the behaviour 
of the protoplasm during the process. The quadripolar 
spindle then is only a special case of ordinary karyokinetic 
phenomena ; instead of two relatively large masses of proto- 
plasm, there are four distinct aggregations, one in every lobe, 
each exercising an independent strain, and the directions of 
the strains may continue separate to the very end of the 
process, or not, according to the form and other special 
circumstances of the cell. 
The existence of the centrosome is, for me, a secondary 
matter. I regard it as a mere insertion point, a granule or 
perhaps a condensation mass ; and thus when it is present, it 
is immaterial whether its origin be nuclear or cytoplasmic. 
It is certain at all events that it may exist either within or 
without the nucleus. Thus in Ascaris megalocephala , var. 
bivalens , the centrosomes are extra-nuclear, whilst in the 
variety univalens 1 , of the same species, the centrosomes, 
together with the whole achromatic spindle, arises within 
the nucleus. The same is true of the spermatogenetic cells 
of some birds, and from Fairchild’s researches on Valonia , it 
1 Brauer, Die Spermatogenese von Ascaris ?negalocephala. Arch. f. Mikr. Anat., 
Bd. XLII. 
