118 PATTEN. fViows cite 
length. The appendages of the sixth pair are short and thick, and have fused 
with each other except at their tips. Just in front of them is a large, deep pit, z.v. 
I do not know of any explanation of the presence of such an invagination at this 
point, unless it may be regarded as an invaginated tail lobe or a telopore, carried 
forward to its present position before the fusion of the last pair of thoracic 
appendages. 
Every trace of the abdomen is absent, something that is very unusual, for it is 
a noteworthy fact that in this class of embryos the abdomen usually remains 
nearly normal, however profound may be the changes that have affected the 
anterior part of the embryo. 
Fic. 41, X 60, sectioned. In this embryo the cephalic lobes and first two 
thoracic segments have disappeared, apparently after median fusion. The primi- 
tive position of the cephalic lobes is indicated by a conical mass of degenerating 
cells projecting into the yolk, and seen in profile on the edge of the egg. From 
the apex of the mass, an irregular train of the same kind of cells, lying deep in the 
yolk, extends backwards to the surface at the anterior end of the embryo. These 
cells probably represent the last remnant of the degenerating oesophagus and 
anterior portion of the embryo. 
The right appendage of the third thoracic segment is absent, and the fifth pair 
is invaginated. Three depressions along the median line are indicated by white 
areas. 
All the parts of the embryo appear very dark, owing to the unusual thickness 
of the cell layers, and the large amount of staining fluid the cells have absorbed. 
FIG. 42, X 60, sectioned. This is a rather common form. ‘The cephalic lobes, 
oesophagus, and first two thoracic metameres are absent. The appendages of the 
first pair are fused nearly to their tips, those of the fourth pair are fused at the 
base only. The two nerve-cords fuse with each other just in front of the fifth pair 
of appendages, and the single median cord thus produced terminates abruptly just 
back of the base of the fourth pair. Within the fused bases of the appendages of 
the fourth segment is a large mass of cells that looks like the remnant of the 
neuromere of this segment, but forced to assume a spherical form by the fusion of 
the appendages. It is connected posteriorly with the rest of the nerve-cord by a 
narrow chain of cells. In front of the fused appendage is merely a thin layer of 
ectoderm and mesoderm, every trace of the nerve-cord being absent. 
Immediately in front of the fused appendages of the third thoracic segment is 
a short, flattened tube, directed diagonally forward into the yolk. It is surrounded 
by a thin layer of mesoderm, and opens outwards by a transverse opening between 
the marginal fold and the anterior edge of the unpaired appendage. It has all 
the appearance of an oesophagus, and probably is one, but of course it is entirely 
out of place here. 
There is a slight asymmetry of the abdomen, due to the absence of one appen- 
dage on the left side, but otherwise the embryo back of the fifth pair of thoracic 
appendages is quite normal. 
FIG. 43, X 60. This embryo is similar to that in Fig. 49. The original position 
of the cephalic lobes is indicated by a shallow, saucer-shaped, ectodermic thicken- 
ing, c./. In the figure, owing to the curvature of the surface of the ovum, it is 
seen edgewise, and only the thickened posterior rim is shown. It is connected 
with the remaining part of the embryo by a broad train of yolk ced/s, lying close 
to the surface. They appear in the figure as a broad, faint band, y.c. The third 
