400 M. Victor Faussek on the Anatomy and 
nucleus in Ziegler’s * sense ; the nuclei, however, do not lose 
their histogenetic property (see below). The study of the 
fragmentation of the nuclei has led me to wonder whether it 
may not be that the so-called “ secondary mesoderm ”’ of the 
Crustacea (Astacus, according to Reichenbach) represents no 
cellular elements, but nuclei in the state of fragmentation. 
6. The mesoderm is formed, as has been stated, from the 
ectoderm; but during the first period of development a few 
elements of endodermic origin are also added to it; these are 
large cells which spht off from the endoderm cells (figs. 13 
and 16). A small number of them separate from the endo- 
derm cells lying peripherally immediately beneath the primi- 
tive streak, and are soon indistinguishable from the cells of 
the latter; for this reason I was unable to ascertain their 
subsequent fate. 
7. It has already been mentioned that the rudiment of the 
germ-cells appears in the ectoderm at a very early period and 
projects into the interior of the ovum. In the earliest stages 
differences in the germinal rudiment may already be perceived 
in certain ova. In some cases the rudiment consists of cells 
with large nuclei, but in others their nuclei do not differ much 
from those of the cells of the primitive streak. The first 
stage in the further development of the rudiment of the sexual 
organs consists in its separation from the ectoderm; its cells 
become superficially covered by a layer of ordinary ectoderm 
cells (fig. 17). In somewhat later stages the rudiment of the 
sexual organs lies sunk in the abdominal nervous system 
(figs. 18 and 19); after the nervous system withdraws into 
the cephalothorax, however, the germinal rudiment remains 
in the abdomen behind the cephalothoracic ganglia, where it 
now appears between two layers of mesoderm, ¢. e. enclosed 
in the ceelom (figs. 19, 20, and 21). In subsequent stages 
the germinal rudiment with the large nuclei considerably 
increases in size, and after the emergence of the embryo serves 
to form the female generative organs (figs. 20, 22, 23, 27, 28, 
and 29). The germinal rudiment of the second kind (that 
which consists of cells with small nuclei) remains of incon- 
siderable size and becomes transformed into the male gene- 
* Ziegler, “ Die Entstehung des Blutes bei Knochenfischembryonen,” 
Archiv f. mikrosk. Anatomie, 830 Bd. While my memoir was in the 
press there appeared the interesting papers of Ziegler on “ Die biologische 
Bedeutung der amitotischen (direkten) Kernteilung im Tierreich,” Biolo- 
gisches Centralblatt, xi. Bd. nos. 12 and 15 {Ann. & Mag. Nat. Hist. 
ser. 6, vol. vili. Noy. 1891, “‘ The Biological Import of Amitotic (Direct) 
Nuclear Division in the Animal Kingdom,” pp. 862-380], and Frenzel, 
“ Zur Beurteilung der amitotischen (direkten) Kernteilung,” zbid, no. 18, 
of which I was unable to avail myself. 
