Fig. 1. 
(96) 
Fig. 2. 
(97) 
Fig. 3. 
(98) 
Fig. 4 
(99) 
PLATE XLI. 
(P. oblongus) from above. Very early stage of ring. [pb = periblast]. The ring has just 
become well defined everywhere and the embryonic fold is seen somewhat bulging centripetally. 
The ring is nearly even in width everywhere, except for being a little wider as it enters the 
embryonic region. 
Width of ring = .02 mm.; in embryonic region = .04 mm. 
Cap almost perfectly circular. Diam. of cap = .55 mm. 
The thick wall (wreath) of periblast is not yet fully covered so that about one row of nuclei 
is seen all around. The number of nuclei could not be accurately determined, so they were 
put in at random guided by what was known of other cases. The outlines of only superficial 
cells (epiblast) are seen, but nuclei of deeper cells are given. The epiblast is seen in profile along 
the margin. The posterior half of the cap is thicker than the anterior, and this is shown by 
heavier dots and lines. The eap should appear convex —but the lithographer could [not] be 
instructed to shade it properly. 
The posterior [lower half of figure] half is the embryonic area, the anterior [upper] the pre- 
embryonic area. 
The ring is now only .02 mm. [in width], later it becomes .12-.15 mm. in width. 
[Section of] cap before appearance of ring, cleavage cavity shallow. 
[Section] just before ring. [be = blastocoele; pb = periblast]. Embryonic area thicker 
than pre-embryonic area. (Large yolk cells supplied). : 
{Section. bc = blastocoele; pb = periblast]. Blastoderm thinned out much in anterior 
half, where for some distance the lower layer is only one cell deep. Towards the anterior edge 
the under layer thickens. 
