VARIATIONS IN LIMULUS POLYPHEMUS. EE? 
EXPLANATION OF PLATE V. 
Fic. 29, X 60. Embryo in about stage £ 
The most striking features are : (1) a diffuse atrophy of the left side, resulting 
in the complete disappearance of the left abdominal appendages and neuromeres, 
and the reduction in size and absence of surface details in the left thoracic appen- 
dages; and (2) the hour-glass form due to a diffuse, transverse atrophy of both 
halves along the fourth thoracic segment. When examined more carefully, it is 
seen that the three anterior thoracic appendages on the right side are nearly 
normal ; the second and third being perhaps a little stouter than usual, but still 
showing all the characteristic details of this stage. The fourth right appendage 
is reduced to a broad, low elevation, probably representing the basal joints of 
the same, the rest of the appendage being reduced to a very small, medianly 
directed protuberance springing from an oval depression. The next appendage is 
larger than the fourth, but smaller and less perfect than the sixth; and that is 
smaller and less perfect than it should be. The last two look as though made of 
wax that had been warmed on the surface, thus melting off sharp angles and 
other details. 
The right side of the abdomen is apparently perfect. 
On the left half of the thorax the chelicera is thrown outwards, but is otherwise 
normal; but the second and third appendages are strikingly smooth and rounded 
on the tips, as though the surface details had been melted off. The fourth is a 
minute papilla, and the fifth and sixth are small, rounded, unjointed elevations. 
The whole left half of the abdomen is absent, except a trace of the marginal 
fold. 
The cephalic lobes are somewhat distorted, and the semicircular lobe is 
apparently interrupted in the median line. 
The median ocellus and the nerves extending to it are very distinct. 
The ventral nerve-cord is not clearly divisible into right and left halves. Back 
of the third pair of thoracic appendages, it narrows, and finally the right half only 
extends beyond the rudimentary fourth pair of appendages into the abdomen. In 
another specimen similar to this, it is very clear that the right half of the cord 
only is represented on the posterior part of the thorax and abdomen. 
The marginal fold is deeply constricted opposite the fourth thoracic segment. 
The right lateral eye and “dorsal organ” lie beyond the limits of the figure, thus 
preserving their normal position in reference to the body of the embryo, but not 
in reference to the marginal fold. The left eye and dorsal organ could not be 
seen, and were probably much reduced, if not entirely absent. 
Fic. 30, X 60, not sectioned. Embryo with two thoracic appendages and 
the corresponding neuromeres of the left side absent. The missing appendages 
appear to be the second and third, as the next three correspond to the last three 
of the opposite side. It should be observed that the second and third appendages 
of the right side are unusually large, as is the case with the appendages on the 
corresponding segments in Figs. 31 and 32. There appeared to be four abdominal 
appendages on the left and only two ontheright. There is a very large peripheral 
vesicle on the right side, /.v. 
FIG. 31, X 60, not sectioned. Embryo with the last three thoracic appen- 
dages on the left side absent. The left half of the abdomen is also absent. The 
