64 



But it is not simply a vestigial relic of prehistoric importance. The 

 great development of entodermal tubules also speaks against the 

 primitive character of the human umbilical vesicle. 



The presence of a large amount of entoderm (tubules, cords and 

 lining epithelium of sac) and considerable hematogenetic activity, to- 

 gether with an extensive network of blood vessels in the wall, seems 

 most intelligible on the assumption of a reptilian ancestry. Thus the 

 histologic structure of the vesicle is to be interpreted in terms of this 

 phylogeny. What was once a very important embryonic organ, has 

 become largely rudimentary. Nevertheless, hematogenesis actively 

 persists for a considerable time and the human umbilical vesicle is 

 more probably the chief source of the origin of the progenitors of the 

 first blood cells. The entodermal cells must be regarded as having a 

 secretory function, their product probably representing a fluid formerly 

 essential in the yolk assimilation. The fact that hematogenesis continues 

 even after the mesenchyme of the liver has begun to function to this 

 end, indicates a very important if not indespensable function for the 

 mammalian umbilical vesicle in blood-cell formation. 



Literature List. 



1) AssHETON, R., The Segmentation of the Ovum of the Sheep, with 

 Observations on the Hypothesis of a Hypoblastic Origin for the 

 Trophoblast. Quart. Journ. micr. Sc, Vol. 41, 1898. 



2) — , Professor Hubrecht's Paper on the Early Ontogenetic Phenomena 

 in Mammals : An Appreciation and a Criticism. Quart. Journ. micr. 

 Sc, Vol. 54, Part 2, 1909, p. 221. 



3) Bailey, F. R., and Miller, A. M., Text-book of Embryology, New 

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4) Bonnet, R., Beiträge zur Embryologie der Wiederkäuer, gewonnen 

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5) — , Lehrbuch der Entwicklungsgeschichte, Berlin 1907. 



6) Branca, A., Recherches sur la vesicule ombilicale de l'homme. Ann. 

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7) Bryce, T, H., The Histology of the Blood of the Larva of Lepido- 

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 Vol. 41, Part 2, 1905, No. 19. 



8) — , Quain's Elements of Anatomy, Vol. 1, Embryology, London 1908. 



9) Gushing, H., The Hypophj^sis Cerebri. Journ. Amer. Med. Assoc, 

 Vol. 53, 1909, No. 4, p. 249. 



10) Dantschakoff, W,, Untersuchungen über die Entwicklung des Blutes 

 und Bindegewebes bei den Vögeln. I. Die erste Entstehung der 

 Blutzellen beim Hühnerembryo etc. Anat. Hefte, Bd. 37, 1908. 



11) Edgar, J. C, Obstetrics, New York 1906. 



12) Eteenod, C. f., Un lecithophore dans l'embryon humain. Bibliogr. 

 anat., T. 5, 1906, p. 247. 



