( 874 ) 



lions at Utrecht concerning this and other erabryologicat problems are 

 always available for comparative and critical work, also for those 

 who do not share my views. Moreover it appears from the literature, 

 mentioned in Weidenreich's paper, that the more extensive and illu- 

 strated article, quoted above, has remained unknown to him. 



All this would not have induced me to return to this subject once 

 more, were it not for the fact that during the last months I have 

 become acquainted with the placentation-phenomena of a totally 

 different mammal in which these phenomena have never yet been 

 studied, namely Galeopithecus volans, which, like Tarsius, Nycti- 

 cebus, Tupaja and Manis, was collected by me in the Indian Archipelago 

 in 1890 — 1891 as extensively as possible for embryological purposes. 

 During the first origin of the placenta of this rare and in many respects 

 primitive mammal l ), phenomena are observed which elucidate the 

 process of blood-formation in the placenta in such an uncommonly 

 clear manner that in this case it will be difficult to deny the evidence. 



The formation of blood in the placenta of Galeopithecus may be 

 said to take place according to a much simpler plan than in Tarsius, 

 although the principal outlines remain the same and here also the 

 non-nucleate haemoglobine-carrying blood-corpuscles must be regarded 

 not as modified cells but as nuclear derivatives. Likewise the placenta 

 of Galeopithecus bears testimony that not only the maternal mucosa 

 but also the embryonic trophoblast takes part in the blood-formation, 

 while the thus formed blood-corpuscles — also those that are furnished 

 by embryonic tissue - - circulate in the maternal blood-vessels only. 



In Galeopithecus the process is simpler especially in this respect 

 that here no megakaryocytes play a part in the formation of blood, 

 so that it is less easy - as Weidexreich did - to regard blood- 

 corpuscles that are set free (such as we notice it in Tarsius, when 

 the big lobed nuclei of these megakaryocytes disintegrate) as being 

 on the contrary devoured in that moment by phagocytosis! 2 ) 



The haematopoiesis is started in Galeopithecus in the following 

 manner. At about the same time that the young germinal vesicle, 

 which has just gone through the two-layered gastrulation stage (gastru- 

 lation by delamination s ) ), has attached itself to the surface of the 

 strongly folded and swollen maternal mucous membrane, this mucous 



!) W. Leche is inclined (Ueber die Saugethiergattung Galeopithecus, Svenska 

 Akad. Handl. Bd. 21, N°. 11, 18*6) to see in Galeopithecus a form which must 

 be placed in the neighbourhood of the ancestral form of the bat. 



-) Sectional series of Tarsius of a later date give a still clearer image than those 

 which served for my figures of 1898. 



s ) See on this point Anatomischer Anzeiger Bd. 26, 353. 



