Embryology of the Phalangiide. 899 
that blastodermic membrane which is produced from the 
blastoderm in many Crustacea (figs. 7 and 11). 
4. The germinal disk arises at one pole of the ovum by 
multiplication of the ectoderm cells. The newly formed 
lower layer of the primitive streak represents the mesoderm, 
since the endoderm is differentiated from the beginning. 
Among the cells of the lower layer a group is separated off 
from the commencement, the cells of which are distinguished 
by their size and peculiar appearance. The separation of 
this group of cells even precedes the formation of the primi- 
tive streak; as early as the time when the ectoderm clothes 
the ovum with a cellular layer this group of cells already 
projects as a little cluster into the interior of the ovum (figs. 9, 
10,11). This cluster lies, as is subsequently to be seen, in 
the posterior portion, although not quite at the end, of the 
ventral streak, and consequently forms a local thickening of 
the ectoderm, which arises almost simultaneously with the’ 
mesoderm, and afterwards furnishes the germ-cells. 
5. The nuclei of the large endoderm cells frequently 
suffered from the effects of the reagents, and then appeared 
to be destitute of a membrane (fig. 8) ; but they were well 
fixed by means of Flemming’s fluid, and presented the 
appearance shown in figs. 7,9, 11, 12, and 13. The nuclei, 
which are figured in Henking’s paper mentioned above, also 
seem to me (at least in some cases) to have suffered from the 
fixative fluids, and therefore to exhibit no membrane and no 
sharp outlines. hat which, for instance, he considers to be 
several nuclei in one cell (vide his fig. 37), I am inclined to 
regard as being nucleoli of a large nucleus, the membrane of 
which is destroyed. At the time of the formation of the 
mesoderm the nuclei of the endoderm become considerably 
larger, so that in comparison with the cells of the germinal 
disk they appear quite gigantic. They possess a sharp con- 
tour and are very poor in chromatin; almost the whole of 
the colourable substance of the nucleus is concentrated in a 
nucleolus, which is very glistening and takes a deep stain. 
We often meet with figures which seem to point to amitotic 
nuclear division (fig. 13) ; it appears that this nuclear division 
is also followed by division of the cell (fig. 12). At any rate 
the endoderm cells never become multinuclear, and even cells 
with two nuclei are rare. I succeeded in determining a 
similar characteristic nuclear structure in the endoderm (yolk- 
cells) of the Araneide also, in the earlier stages of their deve- 
lopment; this had not previously been described by any 
author (Tegenaria, figs. 14 and 15). In Araneide and 
Phalangiide there consequently occurs a fragmentation of the 
