Charles Russell Bardeen 245 
the growing extremities of nerves on their way to muscle cells in the 
regenerating tail of a lizard. The nerve-fibres they describe are com- 
posed first of a chain of cells within which later the axis-cylinder pro- 
cesses become differentiated. They used gold-chloride impregnation in 
their studies. In many respects the growing nerves which they picture 
resemble those which I have seen in mammalian embryos and have 
described above as the “sheath cells.’ I have found that as a rule in 
early embryos the gold-chloride is precipitated, not in the axis-cylinder 
fibrils, but in the stroma of the nerves and in the sheath-cells.” It 
seems, therefore, possible that the cells described by Galeoti and Levi 
were cells which ensheath nerve-fibrils not revealed by the methods they 
used. What they describe as developing axis-cylinders appears some- 
what like a beginning deposit of myelin about axis-cylinder processes. 
For myelin in the early stages of development, gold-chloride has an 
especial affinity. 
Tn general the growing extremities of the nerves within the developing 
muscles resemble those of the skin except that, as a rule, larger bundles 
of fibrils are contained within the nerve-sheaths until the final branch- 
ings take place which serve to distribute fibrils to the individual muscle 
cells composing the muscle bundles. Fig. 8 shows the branching of a 
nerve growing out to supply several muscle bundles of the rectus muscle 
of a pig 39 mm. long. Up to this stage the growing tip of the nerves may 
be easily distinguished in well stained sections. 
The final union of the growing tip of the nerve with muscle-cells 
seems, in the rectus muscle of the pig, to begin in embryos of 8 em., but 
definite endings are few until considerably later. The formation of 
nerye-endings cannot be satisfactorily followed in mammalian embryos, 
owing to the great number and the small size of the cells. So far as [ 
have been able to determine, the steps in the formation of the end-plate 
are as follows: 
An ensheathed bundle of nerve-fibrils extends transversely across a 
number of bundles of muscle fibres. As each bundle is reached an 
ensheathed nerve branch is sent into the midst of the muscle-fibres. 
5 Kaplan has shown that his excellent ink-stain for axis-cylinder processes does 
not stain these in embryos before the appearance of the myelin sheath. The same 
thing seems to be true of the aniline stains for axis-cylinders. In staining Auer- 
bach’s and Meisner’s plexuses with gold-chloride, as a rule the individual fibres 
composing the fibre-bundles are not distinct. The gold seems to be distributed in 
the stroma of the bundles. Apdthy also has called attention to the fact that gold- 
chloride usually stains the stroma of axis-cylinders, but not the contained fibrils 
when used before fixation. For Apdthy’s haematein and gold-chloride stains the 
nerves of mammalian embryos do not seem adopted. 
iy ; 
