SALPIDAB — POEMS WITHOUT COVERING FOLDS. t36 



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

 reduced (Fig. 212 /I) and completely degenerates. This degeneration 

 at tirst affects a zone 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 (" ). 



The above i> in accordance with Salbnsky's earlier description of the fate 

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

 >u^gesi t hat 1 he inner lamella does net disintegrate, hut enters into close con- 

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

 The ectoderm in S. democratica-rmicronata would then have to he traced 

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

 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. -124, and Korotnefk 

 (No. XVIII.) on S. democratica.] 



In the next stage (Fig. 212 B) important differentiations are evident 

 in the embryo. The mesoderm {in) 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 (>i) is also found as a cell- 

 growth proceeding from the ectoderm. Its position marks the plane 

 of symmetry and the anterior end of the body in the embryo.* 

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

 Salkxsky 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 (./■). This is the rudiment 

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

 eo\ ering the placenta. 



The fundamental features of the organisation of the embryo of 

 Salpa, which are thus already sketched out, appeal' 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 



* [Kobotnbpf believes that the aervous system is termed as ;i closed vesicle, 

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

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

 embryonic blastomeres and aol from follicular cells, as Salensky stated. — 

 Ed.] 



