540 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



mistook the secondary for the primary stage, lie gave a 

 very intelligible description of it. 



Remak regarded the completed blood-vascular plexus as 

 the first trace of the system, and as he saw that the vessels 

 were filled with blood, he explained the appearances pre- 

 sented as follows: Cells, he says, coalesce to form cords 

 and plexuses in such a manner that the peripheral elements 

 of each cord coalesce to form a vascular wall, whilst the 

 central ones become blood corpuscles. As a few years later, 

 by means of the silver method, the cell boundaries could 

 be rendered apparent even in the capillaries, the views of 

 Remak appeared to be perfectly well founded. 



Some years ago the island-like rudiments of the blood- 

 vessels were rediscovered by Affanasief, * and I may just 

 mention that the research was conducted under my direction ; , 

 for Affanasief has since stated that his discoveries were not 

 quite satisfactorily made, in which I am unable to agree 

 with him. M. His also soon afterwards expressed himself in 

 favour of the island-like rudiments, and still more recently 

 E. Kleinf has arrived at similar conclusions. Various points 

 which remained doubtful in Affanasief 's researches have been 

 satisfactorily explained by these authors ; and I now proceed 

 to the description of the earliest stages of development of 

 the bloodvessels with the consciousness of being able to treat 

 the question as being finally settled from a morphological 

 point of view. 



If a fresh germ disk be examined at the commencement of 

 the second day of incubation, without any covering glass, with 

 moderately strong powers, isolated cell elements may be per- 

 ceived in the depths of the tissue, in various stages of develop- 

 ment, till they ultimately form large bodies provided with 

 vacuolse, or, in other words, constitute vesicular structures. 

 In optical transverse section, each of these large vesicles 

 gives the impression of being composed of fusiform cells. As 

 the cell increases to form a vesicle, the nuclei in the wall of 

 the vesicle increase also, project towards the cavity of the 



* Wiener Sitzungsberichte, 1866, Band liii. 

 t Wiener Sitzungsberichte, 1871, Marz-Heft. 



