duits de la digestion qui sont assirnilables et qui n'ont pas 

 ete pris par les parois de I'intestin. Ces produits quit- 

 teraient ensuite la cellule pour aller se melanger au sang, 

 dont les corpuscules sont precis^ment extrernernent norabreux 

 autour des anpoules ter.-ninales . " Although Pizon's hypoth- 

 esis would seem the most probable one, as the histological 

 structure of the organ is not such as to suggest a glandular 

 function, still the role played by the "organe r^fringent"' 

 must remain uncertain, until the nature of the liquid con- 

 tained in the tubules is determined. 



THE PERICARDUTI AND HEART. 



Concerning the origin of the common rudiment of the 

 pericardium and heart investigators have given wiaely diver- 

 gent accounts, some deriving it from endoderm, others from 

 mesoderm. Although it is very certain that this structure 

 arises diferently in different Ascidians, still in the buds 

 of one and the same form statements of authors are at vari- 

 ance. Seeliger (29) describes the pericardium as arising in 

 the buds of Glavelina from an enormously large evagination 

 of the ventral portion of the branchial sac, which later be- 

 comes separated as an independent vesicle. He did not, how- 

 ever, distinguish the epicardial sacs, and mistook a part of 

 the latter for the pericardium. Van Beneden and Julin (33) 

 shov,red conclusively that the diverticulixm of the branchial 

 sac observed by Seeliger and called by him the pericardium. 



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