Boyal Microscopical Society. 55 



regular double contour. These chaDges may probably be attributed 

 to the action of the chromic acid. Still, the larger and smaller 

 nuclei could be easily distinguished in the interior of the cells, and 

 moreover, many of the former were observed upon the surface of 

 the membrane, together with a number of blood corpuscles which 

 manifested themselves by their greenish glimmering appearance 

 (Fig. 4). This last examination demonstrated that the anatomical 

 structure of both vesicles in question, was one and the same, — and 

 as there remains no doubt that, in the latter instance, I really ex- 

 amined the umbilical vesicle, one might reasonably suppose that the 

 balloon-like vesicle of the younger ovum — notwithstanding the 

 anomaly of its embryo — represented the same embryonic organ. 



Although further examinations made of similar and fresh speci- 

 mens are absolutely necessary for a final decision, the facts already 

 observed, and being in accord with each other, strongly indicate 

 that the primary birth-place of the coloured blood corpuscles in the 

 human embryo, is to be sought in the above-described gland-like 

 follicles of the umbilical vesicle. 



The origin of these blood corpuscles, according to an older 

 theory, from the axial cells of the embryonic heart and the larger 

 blood-vessels, appears to me as improbable, as their derivation from 

 the axis of certain columns, composed of embryonic cells, and des- 

 tined to the formation of capillaries. It is more natural to suppose 

 that the formation of the first coloured blood corpuscles in the em- 

 bryo occurs, similarly to that of the colourless ones, in the adult, 

 by the medium of certain glandular organs, adapted to this purpose. 

 This view is furthermore confirmed by the established fact, that at a 

 later period of life the former are derived from the latter. According 

 to my own observations, this already takes place during embry- 

 onic life. Neither do the observations, made in the last few years 

 by Klein on the yolk-sac of the chick,* according to which the blood 

 corpuscles originate from cells, arising and separating from the in- 

 terior wall of certain vesicles that are destined to be afterwards con- 

 verted into blood-vessels, correspond with the above-described facts, 

 observed by me. The more recent investigations of Balfour,\ how- 

 ever, regarding the origin of the blood corpuscles and blood-vessels 

 of the chick, seem almost to indicate that the process of formation 

 and multiplication of these bodies in the embryo of birds difiers 

 somewhat from that in man. His statements, confirming, to some 

 extent, those of Klein, correspond very nearly to one of the earlier 

 theories, according to which the blood-vessels in the chick were 

 formed by the fusion of certain stellate cells, and the blood cor- 

 puscles were derived from the nuclei of these cells. 



* Strieker, 'Handbuch cler Lehre von den Geweben des Menschen,' xx., 

 p. 1219. 



t ' Quarterly Journal of Microscopical Science,' July, 1873, p. 280. 



