STUDIES IN MAMMALIAN EMBEYOLOGY. 547 



protruding into the cavity of the fore-gut and marked sp 

 (Entoblast sprossen) in his figs. 53 and 54. It is with these 

 figures that I am inclined to compare the woodcuts which 

 van Beneden has given on pp. 712 and 713 of vol. iii of 

 the ' Anatomischer Anzeiger/ for Vespertilio murinus. 

 In these he figures cellular matter (marked b on p. 713), 

 which at the foremost extremity of these early embryos is 

 meant by him to stand for the bottom of the " Chorda-kanal/' 

 i. e. belonging to the forward growth from the node of Hensen, 

 which we have termed the protochordal wedge (KopfFortsatz, 

 V. Beneden, a. o.). 



In this forward growth the " Chorda-kanal " makes its 

 appearance, and as the Kopffortsatz is intercalated in the 

 hypoblast, the " canal " fuses (beginning in the middle, and 

 from thence both backwards and forwards) with the lumen of 

 the yolk-sac. This intercalating process can be noticed, 

 according to van Beneden, even under the originating pros- 

 encephalon. It is with respect to this point that I must 

 again refer to what I have noticed above when discussing 

 Carius' and Keibel's description of the formation of '' Kopf- 

 fortsatz" and notochord in Cavia and rabbit. 



Here, too, a very rigid inquiry will have to test the facts as 

 stated by van Beneden. The possibility of a pre-existent 

 hypoblastic protochordal plate must be rigorously excluded 

 experimentally before we are justified in giving up the possi- 

 bility that to a certain extent, however much reduced, there 

 might be coincidence between the mammals which Bonnet,, 

 Heape, and myself have investigated, and those which have 

 served for van Beneden' s, Carius', Keibel's, a. o. researches. 

 As stated above, the woodcuts furnish a starting-point for such 

 comparison, which, however, I only bring forward in the very 

 tentative manner here explained. 



In the opossum the earliest developmental phenomena of 

 the notochord were studied by Selenka, and although in his 

 text (' Das Opossum,^ p. 152) he declares himself an adherent 

 of KoUiker's theoretical views, his figures certainly admit of a 

 different interpretation, which if verified would bring the 



VOL. XXXI, PART IV. NEW SER, Q Q 



