350 



Margo acutus auf die hintere Wand der rechten Kammer und teilt 

 sich hier in ihre Endzweige. 



Eine Ursprungsstelle für eine Arteria coronaria dextra war im 

 Sinus Valsalvae der Valvula dextra aortae nicht auffindbar. Nur ein 

 kleines, schwaches Gefäß, welches aus der linken Kranzarterie ent- 

 springt, zieht, sich zwischen Aorta und Arteria pulmonalis durch- 

 schlängelnd, in normaler Verlaufsrichtuug der Arteria coronaria dextra, 

 im Fettlager der Horizontalfurche um die rechte Aurikel herum. Die 

 hintere Wand des rechten Ventrikels wird von Aesten des beschrie- 

 benen anormalen Gefäßes versorgt. 



Resumirend ist noch zu erwähnen, daß das schwache Gefäß in 

 der rechten Horizontalfurche des Herzeus als verkümmerte Arteria 

 coronaria dextra, von der linken Kranzarterie entspringend, zu be- 

 zeichnen ist. 



New York Academy of Sciences. 



Biological Section. December 13th. 



In a paper entitled "Considerations on Cell-Lineage, based on a 

 Re-examination of some Points in the Development of Annelids and 

 Polyclades", Prof. E. B. Wilson presented observations regarding the 

 origin and relations of the mesoblast in annelids and polyclades which 

 illustrate the fact of ancestral reminiscence in cell-lineage. In some of 

 the Annelids (Aricia, Spio, Nereis, and others) the primary meso- 

 blasts have not been properly so-called ; for before giving rise to the 

 mesoblast-bands, they bud forth cells that may be, in some cases, traced 

 into the wall of the archenteron. In Nereis not less than six or 

 eight such cells are formed; these become pigmented, wander into the 

 interior, and finally give rise to the posterior part of the archenteron. 

 In Aricia and Spio only a single pair of corresponding cells is 

 formed, and they are so small as to play a quite insignificant part in 

 the building of the body. A comparison of these results with those of 

 CoNKLiN on Crepidula indicates that the mesoblastic pole-cells of 

 annelids and mollusks are to be regarded both historically and onto- 

 genetically as derivatives of the archenteron, and that the rudimentary 

 cells of Aricia and Spio are vestiges or ancestral reminiscences of 

 such origin. 



A re-examination of the cell-lineage of a polyclade, Leptoplana, 

 shows that as in the annelid or gasteropod, all of the first three quar- 

 tets of micromeres give rise to ectoblast, while the second quartet gives 

 rise also to mesoblast, each cell of this quartet segmenting olf three 

 ectoblast-cells and then delaminating a large mesoblast cell into the 

 interior. The third quartet apparently gives rise to ectoblast alone, 

 though the possibility of its producing mesoblast is not exclused. The 

 four macromeres remaining give rise to the archenteron, as Lanu de- 



