1906] OLIVE—NUCLEAR AND CELL DIVISION OF EMPUSA 253 
among the thallophytes and may be regarded as a primitive form; and 
further, the fact that it possesses intranuclear centers of division may 
perhaps be regarded as adding another point in favor of HERTwic’s 
(’98) view as to the intranuclear origin (by the extrusion of centro- 
some) forming substances from the nucleus of the extranuclear 
centrosomes of the more highly differentiated organisms. 
It has been already pointed out above that Basidiobolus, which 
has been generally regarded as a member of the Entomophthoreae, 
shows in its mitotic features (its broad, multipolar spindles, and its 
formation, according to FAIRCHILD (’97), of a cell-plate), as well as in 
other morphological aspects, wide differences from Empusa. 
Cell-division by means of the growth inward of a ring-formed wall 
is apparently a common type of division among the filamentous thal- 
lophytes. Such a constriction of the cell has so far been shown for 
Beggiatoa (Hinze, :o1), the blue-green algae, Ulothrix (D1rPet ’65), 
Spirogyra (STRASBURGER,’80), Cladophora (Davis,’04), the red algae, 
and a few-other forms. WovycickI (:04), contrary to FAIRCHILD’s 
(’97) assertions, contends that the cell-wall in Basidiobolus also is a 
centripetal growth. The gametes of Sporodinia and the conidia of 
Erysiphe are cut off in a similar manner, except that, according to 
Harper (’9Q), the ingrowth here is simply a deep "narrow furrow and 
not the growth inward of a ring of fungus cellulose. The wall in this 
case is deposited later between the two plasma-membranes. 
As has been shown in this study of Empusa, the ring-formed cleav- 
age-furrow starts at a definite region of the plasma-membrane, some- 
times remote from the nuclei; and further, the nuclei at no time ap- 
pear to be concerned, directly, in the process. ‘TOoWNSEND’S (’97) 
observations on nucleated and enucleated fragments of protoplasm 
leave no doubt, however, as to the ultimate necessity of the presence 
of a nucleus, in order to initiate the cytoplasmic activities in Empusa 
which lead to cell-division. Whether the localized stimulus in this 
case results first in a deposit of a ring of cellulose-substance on the 
inner surface of the wall of the mother-cell, which might then by its 
growth progressively inward be regarded as the agent of cleavage; 
or whether there first occurs in this region an infolding of the plasma- 
membrane, thus resulting in a circular furrow, to be soon followed by a 
deposit of wall-substance in the cleft, Iam not able to state. In either 
