THE EDWAEDSIA-STA&E OF LEBETIIiriA. 295 



The former E. B. Wilson proves to be specially circulatory m 

 function, while the latter are digestive. Studying tlie West- 

 Indian coral Manicina, iu which only the Driisenstreif is de- 

 veloped, H. V. Wilson found that the filament of the first pair of 

 mesenteries arises as a downgrowth of the stomodseal ectoderm, 

 and the later ones from upward reflections of the same layer. 

 He homologizes the simple Madreporarian filament with the whole 

 of the trilobed Actinian filament. From his researches on Aulac- 

 tinia and Rhodactis McMurrich is inclined to agree with B. B. 

 Wilson, and to regard the Driisenstreif as endodermal and the 

 Elimmerstreifen as ectodermal in origin. The sections of Aulac- 

 tinia revealed a bridge of unmodified endodermal tissue between 

 the early filament and the stomodseal ectoderm, but the results 

 with HJiodactis were not so conclusive, although representing 

 earlier stages. 



In this strictly limited aspect of the problem the evidence 

 from Lehrunia at first sight appears incontrovertible. In having 

 the four pairs of mesenteries already developed, along with a 

 nearly solid interior, the larvae present conditions very difierent 

 from those studied by the previous investigators. As already 

 described, no filament is discernible before the gastro-vascular 

 cavity of the adult has begun to be established. And for the 

 next early larvae, the first portion of the free mesentery in the 

 case of the sulco-lateral pair of mesenteries possesses only un- 

 modified endoderm at its free edge, while a filament is well 

 developed below. It is on evidence precisely of this character 

 that E. B. Wilson and McMurrich affirm the endodermal origin, 

 in the former case, of the six ventral filaments of the Alcyonaria, 

 and, in the latter, of the median streak of the Actiuiaria. 



Begarding as I do the lower region of the oesophagus in 

 Lehrunia as a portion of the arehenterou and therefore its lining 

 as endoderm, the significance of its primary relationship with the 

 mesenterial filaments becomes altered from that understood bv 

 the writers just mentioned. 



From such conditions as those revealed in fig. 21, before any 

 ectodermal invagination appears, it is clear that the archenteric 

 endoderm and the filamental tissue are morphologically one and 

 the same. 



I venture to think that in Lehrunia the temporary discon- 

 tinuity in the extruded larvae between the oesophageal lining and 



