THE AMERICAN LOBSTER. 
213 
generally underlie the triangular and U-shaped areas” and are “found as small clouds 
between and also outside the limits of the embryonal tract.” He says further that 
“chromatin grains, as was seen in the surface view, are most abundant where ecto- 
dermal cells are most numerous.” No inference is drawn from this, but plainly the 
true one is not that the larger collection of endoderm cells are centers of cell degener- 
ation, but that the mesoblastic cells attach themselves to those parts of the embryonic 
ectoblast which are growing the fastest, and by their own dissolution give rise to the 
“chromatin nebulae.” 
Bumpus does not explain the origin and fate of the chromatin particles which he 
accurately figures, but remarks that “ structures comparable with the chromatin grains 
of the plasma cells are neither mentioned nor figured by Reichenbach, though the 
so-called ‘serum’ may represent the region of their activity.” Further on it is said 
that “future comparison may prove these,” the “secondary mesoderm cells,” of Reich- 
enbach “to be the same as the plasma vacuoles and their chromatin grains;” and 
again, “I have been unable to find in Homarus preparations that throw any direct 
light on the so-called ‘secondary mesoderm.’” 
I have shown ( 94 ) that the “secondary mesoderm cells” are not cells at all, but 
the products of cell degeneration, and that in their origin and final destiny they bear 
the closest resemblance to the “chromatin nebulae” of the lobster. 
ABNORMAL DEVELOPMENT. 
SEGMENTATION OF THE EGG. 
In every batch of segmenting lobster eggs one is sure to meet with many irregu- 
lar forms, and in some cases the greater number appear to be abnormal. Nuclei can 
be detected at the surface of many of the segments, and if the egg is treated with 
Perenyi’s fluid or with an acid the dark-green segments and their nuclei contrast very 
strongly with a milk-white coagulable substance in which they seem to be embedded. 
Some eggs, which were laid by a lobster on August 23, after a captivity of eight weeks 
in a small aquarium, were light-colored, but were normally fixed to the abdomen, and 
were fertile, although the segmentation was exceptionally irregular. Sections of these 
eggs showed an irregular distribution of cells both at the surface and throughout the 
yolk. In some places cells appear to have been carried below the surface by over- 
growth, and afterwards to have multiplied in the yolk. 
Eggs which are otherwise regularly segmented may contain a large superficial 
mass of undivided yolk, as in fig. 226, plate 50. Here is a very large mass of yolk about 
the pole of the egg — a similar one lay near it on the opposite side — and a considerable 
number of smaller segments. When this egg is sectioned it is found that the large 
yolk masses are nearly devoid of protoplasm, while the smaller segments contain each 
a nucleus which shows traces of degeneration. There is no nuclear membrane, and 
the chromatin has assumed a very irregular form. 
It is common to find eggs with yolk unsegmented with the exception of one or more 
small balls at the surface. Sometimes a single large segment is seen, looking as if it 
had been pinched off, and in this and in many other cases it is evident that the egg 
has in some way received harsh treatment. 
In one egg, rather more anomalous than usual, there was a single small spherical 
segment at one of the poles of the elongated egg, while the remainder of the yolk was 
