64 University of California Publications in Zoology L^ol. 20 



taken place with only a comparatively small amount of new ectoplasm 

 formed in one individual. 



The behavior of the neuromotor apparatus during mitosis is 

 significant in its intimate association with the nucleus. The entire 

 extra-nuclear mechanism which consists of polar centrosome, the 

 astral rays attached thereto and the paradesmose which is stretched 

 out between them as an extranuclear band of large size, is all a 

 direct transformation of the most intimately connected parts of the 

 neuromotor apparatus, the centroblepharoplast, the oblique anasto- 

 mosing fibrils, the lines of basal granules and the attached flagella 

 and cilia. The longitudinal and transverse myonemes simply part 

 at the zone of bipartition of the ectoplasmic territory, without forming 

 an integral part, with structural modifications, of the nuclear figure 

 of mitosis. The comprehensive fashion in which the sum total of 

 the neuromotor system, excluding myonemes, forms the extra-nuclear 

 mechanism of mitosis, is instructive in the matter of the unity of the 

 system, and its integration into an organic complex which survives 

 the shock and readjustments contingent upon mitosis without 

 dedifferentiation and reorganization. This is in marked contra.st 

 with the extent of such dedifferentiation and reorganization in the 

 multinucleate Ciliata, such as Euplotes (Yocom, 1918). 



Another feature of cytological significance is the derivation of the 

 astral rays of the nuclear spindle from what are structurally dis- 

 tinctlj' fibrillar organs, the anastomosing oblique fibers. The ciliary 

 lines which are more granular in appearance in stained material, more 

 homogeneous and distinctly fibrillar in life, also form radiating lines 

 in semicircle from the poles of the paradesmose. The resemblance to 

 the aster of dividing metazoan cells is so striking that one is inclined 

 to regard them as homologous structures. If so, Chambers' con- 

 clusions (1917) that the astere are sol phases of the surrounding 

 cytoplasmic gel present considerable difficulties, as does likewise the 

 fact that the.se fibers in Trichonympha lie in one superficial plane in 

 the surface of the organism, while the asters of the Metazoa are 

 infiltrated through the mass of the cytopla.sm in three dimensions to 

 a much wider extent. The latter difficulty is not insurmountable 

 since it is a logical consequence of the structural specialization of the 

 cell which is the whole undivided trichonymph. It may also be true 

 that with so universal a phenomenon as mitosis pervading all types 

 of living substance, we should expect to find the bipolar organization 

 which appears in the nuclear figure utilizing not one but many diverse 



