232 Miscellaneous. 



inferior blastodermic lamellS, which still remains for a time united to 

 the superior lamella by filaments. Then the axial lamina of Remak 

 is formed, in which M. His distinguishes three parts : — 1, a layer 

 detached from the superior blastodermic lamella ; 2, a layer de- 

 tached from the inferior lamella ; and, 3, an axial cord of union 

 between these two layers. The first two of these parts {inferior and 

 superior accessory lamince) are characterized by vertical striae. The 

 third is designated by M. His the axial cord. These parts give origin 

 to the medullary tube, the dorsal cord, the protovertebrse, and the 

 cephalic and lateral plates. The first indication of the place where 

 the descending aortse will subsequently be situated appears in the 

 form of lacunae behind the rudiments of the protovertebrse. The 

 situation of the heart is marked by a similar lacuna. 



As the superior blastodermic lamella sends prolongations down- 

 wards into the pellucid area, it sends perfectly similar ones into the 

 opaque area. But then these prolongations do not form, properly 

 speaking, a continuous lamella, but they penetrate the subjacent 

 stratum of white vitellus, to form in it a sort of network embracing 

 in its meshes the elements of that vitellus. The tissue thus formed 

 receives from the author the name of circumvallatory tissue (Keim- 

 wallgewebe). Subsequently, in the central part of the opaque area, 

 the superficial layer separates to form the vascular area, whilst the 

 peripheric adherent portion forms the vitelline area. 



In the interior of the circumvallatory tissue there now appears, 

 according to the author, a complete system of lacunae, which, speedily 

 opening one into the other, cut off a thin superior layer. This sends 

 off fiUform prolongations both upwards and downwards. It is the 

 hcematogenous membrane, formed of cells of the archiblast united 

 into a network of which the meshes enclose bundles of cells of the 

 white vitellus. These packets of cells are the starting-points of 

 the formation of the blood-vessels : fusiform cells start from them 

 to penetrate into the subjacent lacunae and clothe them with a 

 continuous endothelial layer ; thence they enter the pellucid area, 

 where they extend themselves in the lacunae between the inferior 

 accessory lamina and the inferior blastodermic lamella ; finally, con- 

 tinuing their centripetal advance, they introduce themselves into the 

 cardiac and aortic lacunae mentioned above, where they arrange 

 themselves in a coil, which merely applies itself to the walls of these 

 lacunae without becoming amalgamated with them. From these 

 primitive vascular walls are subsequently developed all the rudi- 

 ments of vessels, as also the mass from which are derived the con- 

 nective and cartilaginous tissues, and in general all the conjunctive 

 tissues. We may therefore say that, from a genetic point of view, 

 all the conjunctive substances maybe assimilated to the adventitious 

 tunics of the vessels. — Archiv fur miJcrosk. Anat. Band ii. p. 513; 

 Bibl. Univ. August 2.5, 1867, Bull. Sci. pp. 330-332. 



