400
HOWARD A. BERN
cannot ascribe with certainty a function to the caudal neurosecretory
system.
Awareness of the presence of special secretory cells of huge size (see
Fig, 4) in the caudal spinal cord of elasmobranchs (sharks and rays)
began with the correction by Speidel in 1919 of some erroneous conclusions drawn by Dahlgren regarding these cells in 1914. Dahlgren studied
electric rays and reported an association between these special neurons
and the presence of electric organs. Speidel emphasized the constant occurrence of these cells in elasmobranchs whether or not they were capable
of electrogenesis, and further demonstrated the absence of a topographical basis for Dahlgren’s conclusions. It is a commentary on the historical
process that the neurosecretory cells now bear Dahlgren’s name and that
the elucidation of their true nature by Speidel might have been completely forgotten had Ernst Scharrer not “discovered and repropagated
Speidel’s paper in later years. This paper deserves to be considered a
biological classic because it represents the first description of the phenomenon of neurosecretion in animals, and because of the clarity of the
observations and of the experimental analysis. The sophisticated histophysiological investigations of recent vintage have in fact added little to
the fundamentally correct and detailed picture that emerges from
Speidel’s account.
The pioneer findings on elasmobranchs were extended to teleosts in
a later paper by Speidel (1922) and also to ganoids which have received
but little subsequent study. Enami’s contribution (1955, 1959) was to link
these secretory cells in teleosts to a neurohemal organ-the urophysis, a
structure whose existence had been known since the early nineteenth
century. The caudal neurosecretory system thus came to be recognized as
strictly comparable to the cranial ( hypothalamoneurohypophysial) neurosecretory system. Just as Bargmann had earlier clar%ed the mode of operation of the hypothalamic system in vertebrates generally by his concept
of the “neurosekretorische Bahn,” so Enami clarified the mode of operation of the caudal system in teleosts: The Dahlgren cells provide the
neurosecretory nucleus; their nonmyelinated axons provide the neurosecretory tract; and the axon terminals associated with the capillary network provide the storage-release ( neurohemal) organ. Although there is
no urophysis as such in elasmobranchs, there is an extensive neurohemal
area on the ventral surface of the caudal spinal cord.
The caudal neurosecretory system has been subjected to a substantial
number of reviews with various emphases (Enami, 1959; Sano, 1961;
1964; Bern and Takasugi, 1962; Holmgren, 1964; Imai, 1964; Bern et al.,
1965; Peyrot, 1965; Arvy, 1966; Gabe, 1966; Fridberg and Bern, 1968).
The investigator interested in the details of “early” physiological experimentation and of microanatomic analyses should consult these reviews;
HOWARD A. BERN
cannot ascribe with certainty a function to the caudal neurosecretory
system.
Awareness of the presence of special secretory cells of huge size (see
Fig, 4) in the caudal spinal cord of elasmobranchs (sharks and rays)
began with the correction by Speidel in 1919 of some erroneous conclusions drawn by Dahlgren regarding these cells in 1914. Dahlgren studied
electric rays and reported an association between these special neurons
and the presence of electric organs. Speidel emphasized the constant occurrence of these cells in elasmobranchs whether or not they were capable
of electrogenesis, and further demonstrated the absence of a topographical basis for Dahlgren’s conclusions. It is a commentary on the historical
process that the neurosecretory cells now bear Dahlgren’s name and that
the elucidation of their true nature by Speidel might have been completely forgotten had Ernst Scharrer not “discovered and repropagated
Speidel’s paper in later years. This paper deserves to be considered a
biological classic because it represents the first description of the phenomenon of neurosecretion in animals, and because of the clarity of the
observations and of the experimental analysis. The sophisticated histophysiological investigations of recent vintage have in fact added little to
the fundamentally correct and detailed picture that emerges from
Speidel’s account.
The pioneer findings on elasmobranchs were extended to teleosts in
a later paper by Speidel (1922) and also to ganoids which have received
but little subsequent study. Enami’s contribution (1955, 1959) was to link
these secretory cells in teleosts to a neurohemal organ-the urophysis, a
structure whose existence had been known since the early nineteenth
century. The caudal neurosecretory system thus came to be recognized as
strictly comparable to the cranial ( hypothalamoneurohypophysial) neurosecretory system. Just as Bargmann had earlier clar%ed the mode of operation of the hypothalamic system in vertebrates generally by his concept
of the “neurosekretorische Bahn,” so Enami clarified the mode of operation of the caudal system in teleosts: The Dahlgren cells provide the
neurosecretory nucleus; their nonmyelinated axons provide the neurosecretory tract; and the axon terminals associated with the capillary network provide the storage-release ( neurohemal) organ. Although there is
no urophysis as such in elasmobranchs, there is an extensive neurohemal
area on the ventral surface of the caudal spinal cord.
The caudal neurosecretory system has been subjected to a substantial
number of reviews with various emphases (Enami, 1959; Sano, 1961;
1964; Bern and Takasugi, 1962; Holmgren, 1964; Imai, 1964; Bern et al.,
1965; Peyrot, 1965; Arvy, 1966; Gabe, 1966; Fridberg and Bern, 1968).
The investigator interested in the details of “early” physiological experimentation and of microanatomic analyses should consult these reviews;