408 EDWIN G. CONKLIN. 



membrane and they resemble R. Hertwig's "nuclei without 

 chromatin." They are found chiefly in the position of the 

 previous spindle remnants and along the lines of astral radiations. 

 Usually the largest of these achromatic vesicles are in close 

 proximity to the dense mass of chromatin, which in these cases 

 does not become vesiculated. In some instances there is a 

 single elongated achromatic vesicle in each daughter cell which 

 occupies the position of the interzonal fibers of the spindle 

 (Figs. 43-48) and which may inclose the dense mass of chromo- 

 somes at the spindle ends. Such conditions give the appearance 

 of an amitotic division of the nuclear vesicle, but the presence 

 of centrosomes, mid-bodies and in some instances of spindle 

 fibers and astral radiations as well as of chromosomal plates 

 (Figs. 46, 47) clearly shows that these divisions are true mitoses 

 in which the chromosomes have been prevented from absorbing 

 achromatin while the latter has formed a definite boundary or 

 membrane separating it from the cytoplasm. 



Just as the size of a central aster is reduced by the presence 

 of numerous cytasters or parasitic asters which surround it, so 

 the size of the chromatic nuclear vesicle is inversely proportional 

 to the volume of the achromatic vesicles in the cell. It seems 

 practically certain that the chromosomal vesicles and conse- 

 quently the entire chromatic portion of the nucleus grow by the 

 absorption of this achromatic substance. When nuclei are large 

 they contain much achromatic substance and at the same time 

 there are no cytasters or achromatic vesicles in their vicinity; 

 when they are small and densely chromatic there may be cytasters 

 in the cell during the periods of mitosis, or achromatic vesicles 

 during resting periods. "The cytasters are therefore, in my 

 opinion, isolated portions of archiplasm (achromatin plus spongio- 

 plasm) derived in large part from escaped achromatin, which 

 take the aster form during mitosis and the vesicular form during 

 resting periods " (Conklin, 1912, p. 543). 



IV. PERSISTENCE OF NUCLEAR MEMBRANES AND FORMATION OF 

 CHROMATIC CONNECTIONS BETWEEN DAUGHTER NUCLEI. 



It has generally been assumed that one of the strongest evi- 

 dences that amitosis had occurred in any given case was to be 



