106 MALL. [VoL. XIX. 
the normal type. The liver, stomach and intestine are want- 
ing entirely, and the dissociation of the optic vesicle, chorda, 
allantois is almost complete. In this embryo the branchial 
arches and brain show the least changes in them, while the 
rest of the tissues have suffered most. 
Specimens Nos. 302, 309 and 328 are in many respects 
alike and may be considered together. The walls of the brain 
and cord are much folded and fill the central cavity in No. 302, 
while in the other two they are thin, the central cavity being 
enlarged and well filled with round cells, which, however, do 
not all seem to arise from the walls of the nerve tube, for 
their nuclei are smaller, being similar to those of blood cells. 
The tissues of these embryos are pretty well dissociated, 
being composed largely of round cells, within which the out- 
lines of large blood-vessels may be seen. No. 328 has arms 
and legs attached, which have undergone mucoid degenera- 
tion, a well marked cavity, pleuro-peritoneal, and finally rem- 
nants of precartilages which are not fully dissociated. 
In the next embryo (No. 228) the central nervous system 
has also shown itself most resistant. It is markedly dilated 
and the walls are partly dissociated. There are also small 
links of cells present, which remind one very much of the 
growing cord, connecting large masses of dissociated tissue. 
The ventricle is dilated and has within it a large mass of 
dissociated nerve cells. In the face there are two large nerve 
tubes extending from the brain, which no doubt represent the 
eye vesicles and their stalks. The embryo with epidermis 
intact, connects with the degenerated but apparently active 
umbilical vesicle, but not with the chorion. The vascular 
system is represented by a dissociated heart and a large blood- 
vessel, which extends into the umbilical cord. The rest of 
the tissue is a dissociated mass, more or less spotted, being 
composed of a variety of cells, including possibly remnants 
of myotomes. | 
Degeneration of the dissociated structures now follows 
rapidly. In No. 253 the embryo still shows the outlines of 
the pleuro-peritoneal cavity within, but the tissues have be- 
