Embryology of the Phalangiidse. 401 



rative organs (figs. 24, 25, and 26). During the first two 

 months of post-embryonic life the furtlier development of the 

 female germinal rudiment and the transformation of the 

 embryonic germ-cells into egg-cells can be easily traced in 

 young Plialangiidaj (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 2o). 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, I. 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 

 jyi'opria 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 Moina, Ghironomusj 

 and the Aphidte. 



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 raesenteron 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 (stomodasum and proetodasum) 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 amoeboid 



