304 
EDWARD PHELPS ALLIS. 
in the adult, by the nerve of a segment of the body other 
than that from which the muscle itself is developed. 
The proof that Edgeworth offers that this change of 
innervation has taken place in these muscles is : that certain 
muscles that he finds in embryos are developed from certain 
segments of the body ; that these muscles of embryos are 
the homologues of certain muscles described by other authors 
in the adults of the same fishes ; and that these latter muscles 
of the adult are said to be innervated by nerves other than 
those of the segments from which he (Edgeworth) finds the 
muscles of embryos developed. If these several premises 
were all correct, the important conclusion that Edgeworth 
deduces from them would evidently also be, but it is equally 
certain that there is the possibility of error in some one of 
the premises. This seems not to have been given serious 
consideration, and yet Edgeworth’s descriptions of t lie- 
development of these muscles in the Selachii is markedly 
different from Dohrn’s, to whose important work Edgeworth 
makes no reference, and it is well known that the innervation 
of these muscles in the adult has been frequently wrongly or 
incompletely given. Furthermore, I now find that even the 
descriptions of the muscles themselves in the adult Selachii 
are, in certain respects, incorrect. 
Certain anatomists hold that a muscle fibre is, from the- 
earliest embryonic stages, connected with the central nervous 
system by a protoplasmic strand, not yet demonstrable by 
known microscopic methods, which represents a future fibio 
of the motor nerve of the segment, or that a “ something ” 
(Braus, 1905) else establishes that connection. Other anato- 
mists claim that there is no such connection, and that the- 
motor nerve grows outward, independently, from the central 
nervous system, and in some unknown way finds its end organ. 
According to the first of these two views a nerve should, 
in normal conditions, innervate a muscle derived from the 
myotome of its own segment and from that segment only. 
According to the second view the nerve might, in slightly 
changed, if not even in normal conditions, find its end organ 
