No. I.] VARIATIONS IN LIMULUS POLYPHEMUS. lO7 
and a third has imperfectly divided a’-*. The resemblance of the extra append- 
ages to the normal chelicerae, and the fact that all the remaining appendages are 
in their proper positions, remove all doubts as to their identity. 
It should be observed that the fourth chelicera, if this explanation is correct, 
is the oldest, as indeed its size and isolation suggest. This condition, however, is 
the reverse of what usually obtains in segmented animals. There is no distinct 
segmentation of the right cord corresponding to the extra appendages. But if 
present it could not be easily seen, as the segmentation of the nerve-cord in other 
parts of the embryo is very indistinct. But there is a triangular swelling of the 
nerve-cord, .S, which widens forwards, and seems to include the first three append- 
ages of the right side. A small, triangular thickening, posterior and lateral to the 
one just described, lies opposite the fourth chelicera. 
The lateral eye of the left side is normal. But on the right are two dark areas 
which probably represent two right lateral eyes. It would thus appear that the 
right half of the cheliceral metamere has given rise by division to four more or 
less complete half-metameres. 
Fic. 13, X 60. A large embryo in stage C. 
The first two thoracic appendages are absent on the right, causing a spiral 
curvature of the head toward that side. The anal plate forms a conspicuous oval 
protuberance, suggesting the early stages in the formation of the tail in insects and 
scorpions. 
The most singular feature, and one not seen in any other abnormal form, was 
the fact that the cephalic lobes formed a continuous thickened mass of ectoderm, 
without distinction into right and left halves. In the median line was an enor- 
mous wedge-shaped ectodermic thickening, reinforced by an underlying layer of 
mesoderm, extending backward as far as the third thoracic metamere. This 
median thickening seems to be, in part, an exaggeration of a median post- 
oesophageal proliferation frequently seen in normal embryos of this age. On the 
right side of the cephalic lobes mesoderm and ectoderm are indistinctly separated 
from each other, and the former consisted of a mass of the characteristic, degen- 
erating nuclei. In place of the first two appendages on the right, are irregular, 
flattened masses of loose cells containing degenerating nuclei. Nearly all the 
mesoderm of the right side, and especially the great masses in the appendages, 
showed the same kind of degenerating nuclei. None were seen on the left 
side. 
A large area in the yolk, beneath the posterior, thoracic region, and nearly the 
whole surface of the embryo, especially on the right side, was strewn with 
innumerable, intensely red dots, that look like bacteria. But these dots are also 
similar in size and color to the chromatin granules in the yolk nuclei, and also to 
those in the nuclei of certain ectoderm cells. After a careful study of them it 
seems probable that the red dots will turn out to be bacteria, but we must not lose 
sight of the possibility that they may be chromatic granules, liberated by the 
rupture of degenerating nuclei. The granules appear to lead an independent 
existence, at least for a limited period. 
Fic. 14, X 60. A small embryo in stage C.D. 
The right chelicera is absent, and the last two thoracic appendages on the 
right side are completely invaginated. There is a difference in direction of the 
first three and the last three pairs of thoracic appendages, similar to that in 
Fig. 22. 
