SALPIDAE - FOKMS WITHOUT COVERING FOLDS. 425 



It appears that the inner lamella of the brood-sac is very soon 

 reduced (Fig. '212 B} and completely degenerates. This degeneration 

 at first affects a /-one running obliquely round the embryo, leaving 

 only a cap of the lamella covering the anterior end of the embryo and 

 a posterior cup-like portion connected with the rudiment of the 

 placenta, which completely unites with the latter at a subsequent 

 period ; the anterior cap appears soon to disintegrate. The embryo 

 is then covered by only one envelope, the outer lamella of the brood- 

 sac (a}. 



The above is in accordance with SALKNSKY'S earlier description of the fate 

 of the inner lamella (No. 100). The more recent statements of this author 

 suggest that the inner lamella does not disintegrate, but enters into close con- 

 nection with the embryo, finally changing into the ectoderm of the latter. 

 The ectoderm in ,S. democratica-mucronata would then have to be traced 

 back to the transformed epithelium of the oviduct, a view which is a priori 

 improbable, and less in accordance with our own investigations than the older 

 statements. [The ectoderm, like the other embryonic organs, is now generally 

 regarded as arising from the blastomeres. See footnote, p. 424, and KOROTNEFF 

 (No. XVIIL) on S. 



In the next stage (Fig. '21'2 B] important differentiations are evident 

 in the embryo. The mesoderm (m) has appeared between the ecto- 

 derm and the entoderm in the form of a cell-accumulation, which 

 spreads out like a germ-layer to right and left over the sides of the 

 embryo. The central nervous system (n) is also found as a cell- 

 growth proceeding from the ectoderm. Its position marks the plane 

 "I symmetry and the anterior end of the -body in the embryo.* 

 Diametrically opposite to it is another cell-accumulation (I), which 

 SALENSKY also traces back to the ectoderm, and which seems to be 

 the first rudiment of the elaeoblast. That part of the ectoderm which 

 is in contact with the rudiment of the placenta is already distinguished 

 by the large size and the height of its cells (x). This is the rudiment 

 of the lamella, which takes part in the formation of the epithelium 

 covering the placenta. 



The fundamental features of the organisation of the embryo of 

 Snl jut, which are thus already sketched out, appear still more dis 

 tinctly in the following stage (Fig. 213), in consequence of the 

 development of a system of cavities. The inner cell-mass severs 



* [KoROTNKFF believes that the nervous system is formed as a closed vesicle, 

 which lies at first quite independently in the mesoderm without any relation 

 to the ectoderm or to the pharynx. The elaeoblast also arises from the 

 embryonic blastomeres and not from follicular cells, as SALENSKY stated. 

 ED.] 



