1898 - 99 .] Mr T. H. Bryce on Duplicitas Anterior. 
623 
hours under normal conditions, and was the only abnormal embryo 
found in two dozen eggs which were in the incubator at the same 
time. The area pellucida was circular and regular ; the sinus 
terminalis and the vessels of the vascular area were just beginning 
to appear. The blastoderm was removed and fixed in picro- 
sulphuric fluid, the specimen was lightly stained with borax- 
carmine, dehydrated, cleared in cedar oil, and then drawn with 
the camera lucida. 
Figure A represents the embryo viewed from above and magnified 
18 diam. Its length, measured from the head end to the extremity 
of the primitive streak, is 3-7 mm. The anterior end consists of two 
independent members, which diverge from one another at an angle 
of 80°. The right member in the figure is slightly smaller and 
less regular than the left • each has a complete somatopleure and a 
complete splanchnopleure, but the somatopleure becomes single, 
0'3 mm., the splanchnopleure, 0‘4 mm., behind the head end, and 
the neural tubes remain independent for a distance of 0*76 mm. 
From this point to the first somite the neural canal is single, with 
the medullary folds approaching one another, but not meeting. In 
the region where the mesoblast is segmenting, the medullary folds 
are very wide apart, and between them is seen a series of five 
large and regular cubes, forming an azygos series of primitive 
segments. The lateral series have six segments, which are smaller 
and irregular. Posteriorly, where the mesoblast has not segmented, 
but still within the compass of the widely apart neural folds, two 
grooves appear, which run back for some distance parallel to one 
another, then bend towards the middle line, but do not meet. 
The right groove seems to fade away, while the left is continued 
directly into a typical mesial primitive streak. 
Comparison with a normal embryo of the same period of in- 
cubation shows that there has been considerable retardation in 
development. 
The specimen was embedded in paraffin, and a complete series 
of sections obtained 1-200 mm. thick. The remaining figures 
represent certain typical members of the series. 
Notochord . — There are two separate notochords throughout the 
whole length of the embryo, so far as it is differentiated. At 
their posterior ends they become enlarged and pass directly into 
