486 ARTHUR BOLLES LER. 
karyokinetic cell division, the chromatic segments of the 
daughter-stars, after retreating to the poles of the figure, are 
seen to be immediately embedded in cytoplasm; around them, 
but often at some distance from them (see fig. 19, and the 
explanation of it), the new membrane becomes established, 
enclosing both the segments themselves and the cytoplasm in 
which they are engulphed. In other words, at each suc- 
cessive division the elements of the dyasters pitch their tent 
on new ground; they surround themselves with a fence 
enclosing a portion of new territory, and this new territory is 
cytoplasm. 
The nuclear membrane is formed after the same manner as 
the cell-membrane, and has essentially the same structure. 
That is to say, it is pitted but not perforated, and there is no 
communication of any sort between the interior of the nucleus 
and the cell-body. I pass over the chapter on nucleoli, in 
which there are some judicious remarks, and one injudicious 
one—the doubt expressed relatively to Balbiani’s discovery of 
the insertion of the nuclear cord into the nucleoli in the 
“salivary”? cells of the larva of Chironomus. We come 
to the more important matter of the Cytodieresis of 
Arthropods. 
Direct Cytodieresis—This is the only mode of division that 
is found in the adult somatic cells of Arthropods. It is by no 
means infrequent, and may be observed in the most various 
organs. It may also be observed in reproductive cells. 
The process of division is in general extremely simple. The 
nucleus elongates, becomes constricted by a narrow or by a 
broad equatorial furrow, into which the membrane is inflected, 
and which deepens until the separation of the two halves is 
complete. The division of the nucleus is very generally, 
though not always, followed by the division of the cell-body 
(the reader will not omit to notice how important this ob- 
servation is in the face of the summing up of Flemming— 
‘ Zellstz.,’ &c., p. 354—to the effect that the direct division of. 
the leucocytes of Siredon, described by Ranvier, is the only 
case of that mode of division yet proved). And the process is 
