DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 208 
matter is a part of the nuclear network, which is itself con- 
tinuous with the extra-nuclear network. I should be inclined 
to look upon the process as an increase in size or extension of 
the nucleus, such as seems to have been described by Stricker 
in certain leucocytes. 
Pfitzner (14), on the other hand, strongly maintains the isola- 
tion of the nucleus during the whole of its life-history, and he 
recommends certain reagents to demonstrate this fact. But 
inasmuch as he himself admits (p. 72) that these reagents 
produce great changes in the nucleus, his negative conclusions 
cannot be regarded as having so good a basis as the positive 
results of Klein and Leydig, whom I can thoroughly confirm 
in the matter. 
I may draw attention in passing to the similarity of the 
branched endodermal nuclei of Peripatus to the nuclei of 
leucocytes figured by Pfitzner (14, Pl. V, fig. 21). 
I have not been able to distinguish nucleoli in the nuclei of 
Peripatus as distinct from the chromatic thickenings of the 
spongework. Flemming (1) says that nucleoli proper partici- 
pate in forming the chromatic figures in cell division. Flem- 
ming in his work on the cell and cell nucleus (1) has not seen 
the continuity between the strings of the nuclear and intra- 
nuclear spongework. He does not deny its existence but holds 
that it is not proved. 
Flemming makes the important statement that the first 
change observable in a cell whose nucleus is about to divide is 
in the extra-nuclear protoplasm, the fibres of which arrange 
themselves radially around two points on opposite sides and at 
the circumference of the nucleus. Contemporaneously with 
this the nuclear network begins to change, and almost imme- 
diately afterwards the achromatic spindle-fibres appear in the 
nucleus. 
These facts seem to point to the conclusion that the actual 
centre of force, of which the nucleus is the seat, divides first 
and is followed by the re-arrangement of the cell and nuclear 
protoplasm. Flemming considers that the nuclear network 
consists of an achromatic substance containing granules of 
