214 SOME PROBLEMS OF CELL-ORGANIZATION 



I. X Helens and Cytoplasm 



From the time of the earlier writings of Frommann ('65, '67), 

 Arnold ('67), Heitzmann ('73), and Klein ('78), down to the present, 

 an increasing number of observers have held that the nuclear reticu- 

 lum is to be conceived as a modification of the same structural basis 

 as that which forms the cytoplasm. The latest researches indicate, 

 indeed, that true chromatin (nuclein) is confined to the nucleus. 1 

 But the whole weight of the evidence now goes to show that the 

 linin-network is of the same nature, both chemically and physically, 

 as the cyto-reticulum, and that the achromatic nuclear membrane is 

 formed as a condensation of the same substance. Many investi- 

 gators, among whom may be named Frommann, Leydig, Klein, Van 

 Beneden, and Reinke, have described the threads of both the intra- 

 and extra-nuclear network as terminating in the nuclear membrane ; 

 and the membrane itself is described by these and other observers as 

 being itself reticular in structure, and by some (Van Beneden) as 

 consisting of closely crowded microsomes arranged in a network. 

 The clearest evidence is, however, afforded by the origin of the 

 spindle-fibres in mitotic division ; for it is now well established that 

 these may be formed either inside or outside the nucleus, and 

 there is a pretty general agreement among cytologists, with the 

 important exception of Boveri, that both spindle-fibres and astral 

 rays arise by a direct rearrangement of the pre-existing structures. 2 

 At the close of mitosis the central portion of the spindle appears 

 always to give rise to a portion of the cytoplasm lying between the 

 daughter-nuclei ; and in the division of the egg in the sea-urchin 

 I have obtained strong evidence that the spindle-fibres are directly 

 resolved into a portion of the general reticulum. These fibres are 

 in this case formed inside the nucleus from the linin-network ; and 

 we have therefore proof positive of a direct genetic continuity be- 

 tween the latter and the cytoplasmic structures. But more than this, 

 I have found reason to conclude that in this case a considerable 

 part of the linin-network is derived from the chromatin, that the 

 entire nuclear reticulum is a continuous structure, and that it is no 

 more than a specially differentiated area of the general cell-network 

 ('95, 2). This conclusion finds, I believe, a very strong support in 

 the studies of Van Beneden, Heidenhain, and Reinke reviewed 

 beyond (p. 223) ; but the bearing of these only becomes plain after 

 considering the morphological differentiations of the nuclear net- 

 work and its transformations during mitosis. 



1 Cf. Hammarsten ('95). 



2 The long-standing dispute as to the origin of the nuclear membrane (whether nuclear 

 or cytoplasmic) is therefore of little moment. 



