Now t:] VATAATIONS TIN VEIMOLUS POLVPHEMUS. IIg 
pair of appendages are fused at their bases, and back of them terminates the 
ventral nerve-cord. 
The abdomen is smooth and flat, showing no trace of appendages. 
The limits of the mesodermic area are clearly defined by the usual thickened 
rim. The mesodermic area back of the tail lobe is darker, and its posterior 
margin, owing to incomplete concrescence, is deeply notched. 
Fic. 44, X 60. In this embryo the cephalic lobes and the cheliceral segment 
have disappeared, leaving some distance in front of the embryo a large irregular 
patch of cells, continuous right and left with the mesodermic rim. In the figure 
it is seen in profile on the edge of the egg, c./. 
The appendages of the second post-oral segment have fused with each other, 
and a similar fusion of appendages has taken place in the third segment. The 
smaller size of the anterior median appendages indicates that it was formed 
previous to that of the following segment, and has already undergone some 
degeneration. 
The marginal fold, m.f, extends anteriorly between the fused appendages of 
the second and those of the third segment. It usually appears to contract with 
the atrophy of the anterior end of the body, so that it closely encircles all the 
remaining appendages. If that really occurred here, the fold must have in some 
way passed around the second pair of appendages, a process difficult to explain. 
The only alternative is to suppose that a new fold was formed back of the second 
pair of appendages, and that the old one has disappeared or was never formed. 
The nerve-cord terminates as a blunt, unpaired process, a little in front of the 
fourth pair of appendages. The posterior part of the thorax and the abdomen 
are normal, except that the apex of the latter projects freely away from the ovum, 
and the whole abdomen hangs over a great blister-like vesicle filled with fluid and 
enclosed between the blastoderm above and a thickening of the mesoderm below. 
There is nothing in the preparation to suggest that this condition is due to 
shrinkage, etc. 
The outlines of two similar vesicles_(or marginal vesicles) are seen in the 
mesodermic area on either side of the h..u region, m.v. 
Fic. 45, X 60, not sectioned. This embryo shows a slight reduction of the 
cephalic lobes and of the third and fourth thoracic appendages of the right side. 
In place of the fifth and sixth appendages and the abdomen, is a large median 
conical protuberance. Whether the latter represents the fused fifth and sixth 
appendages or the tail lobe could not be determined. 
Fic. 46, X 60, not sectioned. The cephalic lobes have disappeared, or at 
least together with the oesophagus are reduced to an invaginated, conical layer of 
cells, constituting the dark mass at the apex of the V-shaped marginal fold, d.c./. 
The chelicerae have fused to form a short median process, which lies in a 
depression that in front is partly overarched by a semicircular fold of the 
ectoderm. 
The appendages of the second pair have fused to form a very long, slender, 
corkscrew-like filament. It is attached to the embryo just back of the apex of 
the fused chelicerae. The appendages of the third pair are fused at their bases 
and somewhat diminished in size. The nerve-cord terminates abruptly just back 
of them. 
The parts of the embryo lying back of the third thoracic segment are prac- 
tically normal. 
