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SUMMARY OF CURRENT RESEARCHES RELATING TO 
on the boundary lines of the transverse muscle-septa and the subperi- 
toneal connective tissue, apparently in direct connection with the rudi- 
ments ( Stiimpfen ) of the ventral arches; but the ribs of Selachii, 
Amphibia, and Amniota arise on the boundary lines of the transverse 
and the horizontal muscle-septa, quite independently of the vertebral 
column. 
Beginning with ancestral forms (a), (6), and (&'), with ribs which 
lay between the dorsal and ventral muscles, Babl supposes these to 
have been lost in c' and c", and to have been replaced by subperitoneal 
skeletal parts (“ pleural arches ” of Goette). On the other hand in the 
ancestral form (c) these pleural arches must have been formed along 
with the ribs inherited from ( b ') and (a). In a separate chapter Prof. 
Rabl enters upon a discussion of the origin of limbs, but the memoir is 
not yet fully published. 
Yolk-Organ of Vertebrates.* — Dr. Hs. Virchow continues his 
account of the “ yolk-organ.” The yolk-sac entoblast of reptiles has a 
double origin, from the one-layered parietal epithelium and from the 
yolk-cells. These are separated by the perilecithal cleft. The parietal 
epithelium appears in two forms, as ripe epithelium with high cells, 
and as early epithelium with flat cells on the proximal wall of the 
yolk-sac — the roof of the subgerminal cavity. Preceding the mature 
one-layered epithelium there is the layered epithelium ; preceding the 
layered epithelium there is the formation of cells in the yolk ; and 
* Archiv f. Mikr. Anat., xl. (1892) pp. 39-101 (2 pis.). 
