368 



SCIENCE. 



[N. S. Vol. XX. No. 507. 



'die von mir, Trophoblast genannte Keim- 

 sehicht ist * * * die aussere schieht der 

 Saugethierkeimblase welche vor der defini- 

 tiven Ausbildung des formativen Bpiblastes 

 dieses sowie die Hypoblastanlage umhiillt 

 iind an der Bildung des Embryos iiber-. 

 haupt keinen Antheil nimmt.' 



In this last paper I have for the first 

 time asserted that in my opinion the Sauro- 

 psidan arrangement, as well as that of the 

 Ornithodelphia, can not possibly be looked 

 upon as ancestral to what we find in the 

 monodelphie (and didelphic) mammalia 

 and that, on the contrary, the trophoblast 

 (L c, p. 57, No. 7) is a precociously segre- 

 gated larval envelope which encloses an 

 inner cell mass, out of which the embryo 

 is going to be built up. I have at the same 

 time drawn a comparison between the 

 mammalian trophoblast and the 'Deck- 

 schicht' in amphibian development and 

 have also drawn attention to those cases 

 where remnants of a trophoblastic layer 

 could be detected in the Sauropsida. 



Only in 1902, however, have I gone yet 

 further back, and leaving the recent am- 

 phibia out of the ancestral line, I have 

 attempted to draw a comparison between 

 the trophoblast (and the other fcetal mem- 

 branes coexistent with it) of the Amniota 

 and larval envelopes of invertebrate prede- 

 cessors (Verhandl. der Eon. Akad. v. Wet- 

 enschappen te Amsterdam, Vol. VIII., No. 

 6, 1902, p. 53). Alinea! It has now been 

 shown that since the first introduction of 

 the name trophohlast sixteen years ago my 

 own definition and interpretation of it has 

 not undergone any alteration, although ad- 

 vances have been made in the appreciation 

 of its theoretical significance. 



And it is for this reason difReult for me 

 to understand that the name has been mis- 

 understood both by embryologists and by 

 gynaecologists, even to such an extent that 

 the writing of the present article seems 

 necessary to prevent further confusion. 



So, for example, Charles S. Minot's defi- 

 nition of the trophoblast on p. 100 of his 

 'Laboratory Text-book 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, etc., are likewise in com- 

 plete disaccbrdance with the original defi- 

 nition, such as it was substantiated by the 

 different quotations given above. 



In attempting to explain for myself how 

 IMinot can have fallen into this error — 

 from which consultation of the papers 

 above quoted would have withheld him — 

 I can not but suppose that Bonnet's 

 'Grundriss der Entwiekelung der Haus- 

 saugethiere ' must have led him astray. In 

 this we find on p. 31 a woodcut (Pig. 

 17), in which the trophoblast (Bonnet's 

 primarer Ectoblast) is represented as a 

 separate layer outside of the ectoderm of 

 the monodermic blastocyst of the hedge- 

 hog and which woodcut is marked 'naeh 

 Hubrecht,' although I never published 

 anything of the kind, nor in my writings 

 have 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 with- 

 out any ambiguity. Already on p. 19 

 of my paper of 1895* have I caUed atten- 

 tion to the fact that Bonnet's woodcut was 

 a misrepresentation of my own views and 

 have on Plate IV., Fig. 81, reproduced a 

 hardly known figvire of KoUiker's of the 

 rabbit's blastocyst, which, on the contrary, 

 is in complete accordance with those views. 

 Misrepresentations, however, are hard to 

 kill. 



In Hertwig's 'Handbueh der vergl. Ent- 



* VerJiandel. Kon. Akad. Amsterdam, Vol. IV., 

 No. 5. 



