128 PATTEN. 
Fic. 68, X 60, sectioned. In this embryo the cephalic lobes and cheliceral 
segment have disappeared, except for a cloud of degenerating cells in the underlying 
yolk. These cells lie where the cephalic lobes ought to be, and perhaps they repre- 
sent the remnants of these organs ; but, on the other hand, they have more the 
histological character of loose mesoderm cells, and are produced, in part, at least, 
by the concrescence of the thickened anterior margins of the mesodermic area ; 
they thus resemble the post-anal band formed by the concrescence of the posterior 
margins of the mesodermic area. This anterior band of cells gradually becomes 
more dense posteriorly, till it finally merges into a flattened, oesophagus-like 
invagination, which opens just over the anterior margin of the fused second pair 
of appendages, ve. 
A remarkable feature of this embryo is the curious invagination extend- 
ing along the whole left margin of the mesodermic area, 7.m.a. This very 
narrow-mouthed infolding converts the mesodermic rim into a thin shelf of 
cells, projecting deeply into the yolk. In most sections the cavity of the 
invagination is very plain, and it is then seen to be lined with a continuation of 
the thin surface cuticula. (See sections, Pl. XI, Fig. 68.) 
Along this furrow, and in the margin of the aborted cephalic lobes, the surface 
of the ovum is covered with masses of minute, intensely red dots that look very 
much like bacteria. The dots are also found just below the surface, and then it 
often appears as if some of the nuclei had ruptured, allowing a swarm of chromatin 
granules to escape. 
The second pair of appendages have fused, forming a broad, biloped plate back 
of which the nerve-cord terminates. The fifth and sixth appendages of the left 
side are absent. The abdomen is absent ; in its place is a very deep, thick-walled 
depression. The marginal fold is very thick posteriorly, and terminates abruptly 
in a foot-shaped enlargement that dips down into the depression, and forms a part 
of its lateral wall. The posterior end of the right marginal fold is weak, and is 
not connected with the fold on the opposite side. 
The dark area back of the abdomen, /.a.c., represent a great cloud of cells lying 
in the yolk, and formed by the concrescence of the posterior portions of the 
mesodermic rim. 
Fic. 69, X 60. Embryo with nearly circular mesodermic area. The nerve-cord 
appendages and cephalic lobes have disappeared. 
At the anterior end is a mass of mesoderm with a conical cloud of yolk cells 
beneath, so faint as to be hardly visible in surface views. From this point the 
longitudinal, ecto-mesodermic band, gradually increases in distinctness toward the 
posterior end, where the two layers that compose it are sharply separated. The 
outer layer is here raised to form the median protuberance, which probably 
represents an enlarged tail lobe. The outline of the mesodermic area is clearly 
defined, and along its lateral and posterior margin are numerous irregular masses 
of cells that extend deeply into the yolk. 
The tissues appear healthy and normal, but there is no trace of organs other 
than the median appendage. 
