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2 Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
Descriptions of the Embryos figured. 
The embryos were in most cases fixed in the corrosive-acetic acid mixture of FLEMMING, although 
a few specimens were fixed in ZENKER’s fluid, in chromo-acetic acid, and in picro-sulphuric acid. In every 
case the drawings were made from the specimens when preserved in 80°, alcohol. Figures I to 24b 
inclusive are drawn at a magnification of eight times the actual size of the specimens. The remaining 
figures, 25 to 32b inclusive, are drawn at a magnification of five. H.E.C. is an abbreviation for Harvard 
Embryological Collection. 
Fig. 1. Blastoderm, 3.0 mm. in length. Normal plate series No. ı. H.E.C. 986. Dorsal view. X 8. 
The blastoderm is elongately oval in outline and bluntly pointed at the posterior end. Its length 
is 3.0 mm. — its greatest width 1.5 mm. The disc is raised slightly above the surface of the surrounding 
yolk. The segmentation cavity causes a rounded swelling in the median line, 0.5 mm. from the posterior end. 
This swelling is approximately 0.3 mm. wide and 0.6 mm. long, with its longer axis placed at right angles 
to that of the blastoderm. 
Fig. 2. Blastoderm, 4.2 mm. in length. "Normal plate series No. 2. H.E.C. 989. Dorsal view. X 8. 
The blastoderm is broadly oval in outline, a little narrower posteriorly than anteriorly. Its greatest 
length is 4.2 mm. Its greatest width — a little anterior to the middle of the disc — is 3 mm. The segmen- 
tation cavity forms a swelling almost circular in outline and approximately 0.4 mm. in diameter. The margin 
of this swelling is best defined anteriorly. The posterior margin lies 0.4 mm. anterior to the posterior rim 
of blastoderm. The posterior margin of the blastoderm is a little thickened near the median line. 
Fig. 3. Blastoderm, 4.4 mm. in length. Embryo 0.3 mm. in length. Normal plate series No. 3. 
H.E.C. 990. Dorsal view. X 8. 
The blastoderm is broadly oval in outline. Its greatest length is 4.4 mm.; its greatest width 3 mm. 
The rim of the blastoderm is thickened around the entire circumference, but the thickening is most marked 
posteriorly. The embryo appears as a rounded thickening projecting forward in the median line 0.3 mm. 
from the posterior rim of the blastoderm. The embryonic thickening becomes narrower on either side 
of the median line and passes over, without distinct lateral boundaries, into the posterior rim of the 
blastoderm. There is a very shallow indentation, the rim notch, in the posterior edge of the embryonic 
thickening. 
Fig. 4. Embryo 1.4 mm. in length. Normal plate series No. 4. H.E.C. 983. Dorsal view. X 8. 
Only a small portion of the blastoderm immediately surrounding the embryo is shown in this figure. 
The embryo appears as a thickened plate extending forward a little over 1 mm. beyond the thickened rim 
