6 
MONICA ^rAYLOK. 
space, but the series is a slightly older one than tlie paraffin 
series. In tlie embryonic rudiment, as seen in a celloidin 
section, the thickened neural plate covered by ectoderm lies 
over an ill-defined endoderm, the yolk syncytium separating 
the latter from the yolk. The rest of the blastoderm is now 
two cells deep except at its advancing edge, where it is still 
thick. 
Text-pig. 1. 
A microscopic preparation of the blastoderm of an egg of Stage 
10, removed from the underlying yolk, stained, cleared and 
mounted in balsam. 
Stage 11 is illustrated by Plate 1, fig. 3. The blasto- 
derm is gradually extending over the egg, becoming much 
thinner as it does so, as though the increase in surface area 
Avere at the expense of depth. The embryonic rudiment 
is elongated to form a white streak, which is broad at the 
anterior end, narrower in the middle, and broader again 
where it gradually fades into the blastodermic rim. The 
elements forming this streak appear, in sections, to be very 
much pressed down by the outer ectoderm. 
