108 



cologists, even to such an extent that the writincr of the present article 

 seems necessary to prevent further confusion. 80, for example, Sedg- 

 wick Minot's definition of the tropho blast on p. 106 of his Laboratory 

 Textbook of embryology (1903) as: "a special layer of cells developed 

 on the outer surface of the ectoderm of the mammalian blastodermic 

 vesicle" is both wrong and misleading. Several statements in the same 

 paragraph on p. 107, e. g. that the trophoblast is sometimes developed 

 only later, that it disappears when the placenta is being formed &c., 

 are likewise in complete disaccordance with the original definition, such 

 as it was substantiated by the different quotations given above. 



In attempting to explain for myself how Minot can have fallen into 

 this error — from which consultation of the papers above quoted would 

 have withheld him — I cannot but suppose that Bonnet's "Grundriß 

 der Entwickelung der Haussäugetiere" must have led him astray. In 

 this we find on p. 31 a wood-cut (Fig. 17) in which the trophoblast 

 (Bonnet's primärer Ektoblast) is represented as a separate layer outside 

 of the ectoderm of the monodermic blastocyst of the hedgehog and which 

 wood-cut is marked "nach Hubrecht" although I never published any- 

 thing of the kind. Nor in my writings have I ever, as we have seen 

 above, given the slightest justification to an interpretation so entirely 

 inconsistent with my own views which have repeatedly been expressed 

 without any ambiguity. Already on p. 19 of my paper of 1895 (Ver- 

 handel. Kon. Akad. v. Wetensch. Amsterdam, Vol. 4, No. 5) have I called 

 attention to the fact that Bonnet's wood-cut was a misrepresentation 

 of my own views and have on PI. IV Fig. 81 reproduced a hardly 

 known figure of Koelliker's of the rabbit's blastocyst, which on the 

 contrary is in complete accordance with these views, IMisrepresentations 

 however are hard to kill. 



In Hertwig's Handbuch der vergleichenden Entwickelungslehre 

 der Wirbeltiere (Bd. I, p. 917) and in Weber's Säugetiere ip. 284) 

 similar transpositions of my intentions in insisting on the recognition 

 of a distinct trophoblast have not crept in. I cite from Hertwig: "Die 

 verschiedene Entwickelung des Trophoblastes hat Hübrecht in folgenden 

 Sätzen kurz zusammengefaßt: 



"Die von mir Trophoblast genannte Keimschicht ist für die An- 

 heftung des Säugetierkeimes an die mütterlichen Gewebe in erster Linie 

 bestimmt: dabei entwickeln sich zu gleicher Zeit in der mannigfaltigsten 

 Weise lokalisierte oder über die ganze Oberfläche sich erstreckende 

 Wucherungen, welche zur Ernährung des Embryos dienen." — „Der de- 

 finitive formative Epiblast, welcher als sogenannte Keimscheibe oder 

 Embryonalschicht auf der oberen Fläche der Keimblase hervortritt, ist 

 zur Zeit seines ersten Auftretens nie an der Oberfläche gelegen, sondern 

 immer von Trophoblastzellen überlagert." 



"Die Art und Weise, wie diese Ueberlagerung des formativen Epi- 

 blastes durch Trophoblastzellen ein Ende nimmt, ist sehr verschieden; 

 entweder entsteht zwischen Epiblast und Trophoblast ein persistierender 

 Raum, welcher etwas später zur Amnionhöhle wird (Erinaceus, Arvicola), 

 oder es tritt eine engere Verwachsung von den Epiblasträndern mit dem 

 Trophoblast ein, worauf ein Durchbruch der deckenden Trophoblast- 



