208 BULLETIN :, MUSEUM OF COMPARATIVE ZOOLOGY. 
tion of nerve fibres, but also their distribution in the central nervous 
system. Gaskell (89) has rightly insisted that the position of the cell 
groups which are in connection with the nerve fibres, is the true crite- 
rion of what forms a nervous metamere, rather than the position of the 
exits of the nerve fibres. The shifting of nerve roots is too well known 
to need discussion here. In regard to sensor nerves Miss Platt (?96) 
says: “Both development and comparative anatomy tend to show 
that it is a matter of little moment whether these fibres [of the lateral- 
line nerves] enter the brain by one nerve root or another.” I find as a 
result of my own studies that the ganglionic cells of cranial nerves enter 
into fibrillar relation with the neural tube at points quite widely sepa- 
rated from the encephalomere from which the cells were proliferated, 
and also that in embryos of different Vertebrates the relations of the 
fibres of the same nerves to the encephalomeres are variable, not only 
in the case of ganglionic roots but of medullary roots also, as those of 
the trigeminus, abducens, and glossopharyngeus. In the swine and the 
chick the abducens arises from encephalomere VI, whereas in 5. acan- 
thias it is in relation with encephalomere VIT. Also in swine and chick 
the root of the glossopharyngeus is in relation with encephalomere VII, 
whereas in S. acanthias it passes from the neural tube posterior to this 
neuromere. It is obvious, then, that we must take into consideration, 
particularly in the case of cranial werves, both the location of the 
«Kerne ” of the medullary roots, and the points or regions of prolifera- 
tion of the ganglionic cells of ganglionic roots, in order to determine 
their primitive relationships. 
a. HISTORICAL REVIEW. 
An examination of the literature bearing on the question of the re- 
lation of nerves to neuromeres is rendered difficult by the fact that 
many investigators have failed to distinguish between medullary and 
ganglionic nerve relations, and thus have not made clear what they 
meant by the statement that a nerve “develops” from, or has its 
“origin” from, the expansion or constriction of a neuromere. The 
figures of McClure (90) and of Waters (92), for example, show a pro- 
liferation of the ganglionic Anlagen of nerves from the neuromeres, but 
not the relationship of the neuromeres to nerve fibres. While it seems 
very probable that the proliferation of ganglionic Anlagen has a bearing 
on the primitive relationship of the dorsal nerves (sensor portion), our 
best criteria of the segmental value of encephalomeres, as well as of 
myelomeres, is their relation to medullary nerves, — i. e. ventral nerves 
