Embryology of the Phalangiide. 401 
rative organs (figs. 24, 25, and 26). During the first two 
months of post-embryonic life the further development of the 
female germinal rudiment and the transformation of the 
embryonic germ-cells into egg-cells can be easily traced in 
young Phalangiide (figs. 27 and 28). I did not succeed in 
investigating the final development of the male germinal 
rudiment ; in young harvest-men the latter appeared as a 
tolerably small group of cells lying in the abdomen immedi. 
ately behind the nervous system, and, like the female rudi- 
ment, separated from the latter and from the body-wall by a 
layer of loose connective tissue (figs. 25 and 25). In size 
the male rudiment is far inferior to the female during the same 
period of development. These embryonic germinal rudiments 
form in the first place the commencement of the actual germ- 
glands, 7. e. ovary or testis as the case may be; other portions 
of the reproductive organs, male as well as female, are com- . 
pletely wanting at the time when the young emerge, and 
their formation devolves entirely upon the post-embryonic 
development. The female as well as the male germinal, 
rudiments are enveloped in an extremely delicate membrana 
propria containing very small scattered nuclei. In Phalan- 
gium therefore there takes place a very early separation of 
the germ-cells, similar to what we find in Motna, Chironomus, 
and the Aphide. 
8. The endoderm cells preserve their general form and 
structure without any changes worthy of remark until the 
later stages of development; they merely become somewhat 
smaller. But the fragmentation of the nuclei continues for 
only a limited period. When the nervous system begins to 
develop the nuclei of the endoderm cells have already lost 
the characteristic signs of fragmentation; they have now 
become smaller and no longer possess their former peculiar 
structure. The definitive formation of the mesenteron takes 
place quite at the end of the embryonic development, after 
the external form of the embryo is already complete, the 
nervous system concentrated in the cephalothorax, and the 
portions of the alimentary canal which are derived from the 
ectoderm (stomodeum and proctodeum) are fully developed, 
The visceral layer of the mesoderm forms folds, which pene- 
trate deep into the yolk and divide it into separate masses 
(the subsequent hepatic sacs). The central portion of the 
yolk remains undivided and forms the actual mesenteron. 
At the close of the embryonic development the endoderm 
cells appear to undergo a process of degeneration ; they lose 
their contour and the yolk-spherules lie at liberty ; in some 
cases small roundish nuclei, which are sometimes amceboid 
