123 DR. fl. KLEIN. 



likewise he is not coireet in making it stop at an outer 

 angle, for this prismatic annular mass is only the thickened 

 portion of the original parablast. For the sake of simplicity, 

 however, we will henceforth consider under the name of 

 parablast only this prismatic rim. Its greatest thickness is 

 about 0'12 mm.; its lower surfaces, i.e. its internal and 

 external surface (contrary to the assertion of Bambeke) rest 

 on the yolk, with which they are in very close connection, 

 the parablast being, as it were, moulded into the jagged surface 

 of the yolk ; the upper surface of the parablast is free, and 

 appears in hardened sections bordered by a very sharp out- 

 line as if by a membrane. 



The substance of the parablast is a finely granular material, 

 containing isolated, minute yolk granules, which become 

 larger nearer to the yolk ; on account of this the line of 

 boundary between parablast and yolk cannot be at all points 

 made out with precision. In the very superficial parts, and 

 also at some places of the deepest parts, I think I can 

 recognise faint outlines of what corresponds to nucleus-like 

 bodies. 



In a later stage (fig. 3) the archiblast is seen to be still 

 biconvex (slightly thicker at one edge), and much broader 

 than in the former case (over 1"5 mm.); its thickest 

 diameter being, however, smaller (0*4 mm.). The most 

 superficial layer of its cells is very conspicuous, and appears 

 almost separated from the rest by a thin cleft. This sepa- 

 ration, as we shall see, remains persistent in the following 

 stages, and to it is due the difierentiation of the corneous 

 layer from the nervous layer of the epiblast (see Rieneck's 

 paper, my first communication, and Strieker's article, men- 

 tioned above). 



The archiblast is very well defined from the yolk of the 

 saucer-like depression. The yolk possesses the same morpho- 

 logical characters as in the former case. The parablast, 

 however, has changed considerably : (a) it has become more 

 finely granular and transparent, thinner, and at the same 

 time broader ; it resembles now a mass of a more placoid 

 shape, which is wedged in for a certain distance (see fig. 3) 

 between the archiblast and yolk ; at the same time bearing 

 the same close relation to the yolk as in the former case. 

 That this wedge-like process of the parablast is due to an 

 active ingrowth of the latter, and not merely to the circum- 

 stance that the archiblast, while growing in breadth, spreads 

 over and heyo7id the inner edge of the parablast, is clearly 

 proved by comparative measurements ; (l) in many sections 

 its superficial layers are, over greater or smaller areas, of a 



