110 PATTEN. [Vou. XII. 
The prominent mesoblastic rims of this type of embryo are subject to local 
vesicular enlargements, which are usually filled with a clear fluid and lined with 
several layers of rounded cells derived from the mesoderm. The round cells 
present all stages of degeneration. 
The individual characteristics of these embryos are as follows : 
Fic. 16, X 60, sectioned. Two thoracic metameres are absent, probably the 
first two. Last three pairs more or less invaginated at apex. Embryo somewhat 
elevated as a whole, but depressed in centre, and surrounded by a high, thick, 
marginal fold. Abdomen absent. Cephalic lobes, sharply depressed below level 
of rest of nervous system, forming a steep descent between the first two appen- 
dages. ‘Two deep oval invaginations on the lateral margins of the cephalic lobes. 
There is a slight depression at the summit of the elevation between the first 
two thoracic appendages, from which arises by inward proliferation, a great mass 
of degenerating cells, which give this area its dark color. The region of most 
active proliferation seems to extend a short distance along the median line, the 
crowd of cells thus produced mingling anteriorly with those about the oesophagus, 
and diminishing posteriorly till they disappear about opposite the anterior margin 
of the second pair of appendages. 
The mesodermic area is extensive anteriorly, but without a conspicuous rim, 
which was too remote from the body of embryo to represent in the figure. Two 
broad masses of mesoderm radiate from the head of embryo to the rim of the 
mesodermic area. Posteriorly the mesodermic rim is well marked and notched in 
the median line, where there is a small ectodermic elevation, /#.a.c., continuous 
with a great mass of underlying yolk cells. The latter are also continuous with 
the great cloud of cells arising from the deep oval invagination, ¢./., in the anal 
plate. There isa small marginal vesicle on the right side, #.v. No trace of 
segmentation in the mesodermic area. 
Fic. 17, X 60, sectioned. Embryo short and rather broad. Abdomen absent. 
Marked difference in size of the first, the following three, and the last two, pairs 
of appendages. Cephalic lobes broad and disproportionately large. Large oval 
depressions, 67. 7v., on sides of lobes partly covered by an overhanging ganglionic 
‘fold. Marginal fold conspicuous posteriorly, where it extends across the median 
line, forming a very prominent spindle-shaped enlargement. No marked con- 
crescence of the posterior margin of the mesodermic area. 
Fic. 18, X 60, sectioned. The body of this embryo lies well below the sur- 
face and is much compressed laterally, so that the nerve-cord forms a single, 
median, roof-like ridge, not adequately represented in surface views. The 
cephalic lobes are absent, but there is a small median invagination, probably 
representing the oesophagus. 
There is a very large tail lobe, projecting upward and forward, and entirely 
separated from the body except at its posterior end. Its interior is filled with 
yolk. On either side are seen the median portions of two great marginal vesicles, 
m.v. The outer margins of the vesicles coincide with the peripheral margin of 
the mesodermic area. In the depressions beneath the legs and the tail lobe, on 
the nerve-cord and elsewhere, the surface of the embryo was covered with clusters 
of the intensely red dots that look so much like bacteria. 
Beneath the base of the tail lobe is a conical invagination best seen in sections, 
directed diagonally backward into the yolk. From its posterior end, streamers of 
closely packed cells extend into the yolk. Around these streamers are many free 
nuclei resembling yolk cells. 
