2. THE NEUROHYPOPHYSIS
145
its pharmacological spectrum. Partition chromatography did not distinguish the Hydrolagus neutral peptide from oxytocin, but in this case
multiple biological assays against oxytocin itself showed a close parallel
between the properties of the two active agents. It must be concluded
that present evidence suggests that oxytocin is the natural, neutral principle of Hydrolagus colliei, but no final decision will be possible until this
is confirmed by chemical analysis.
The presence of arginine vasotocin in Hydrolagus colliei is not a surprising finding, and the low proportion of this principle is reminiscent of
the situation in the elasmobranchs. However, the possible presence of
oxytocin in the holocephalians is a remarkable observation, since this
principle is most closely associated with the mammals and its existence
so early in the vertebrate tree is not in accordance with current theories
of neurohypophysial evolution (Acher et al., 196%). It is another example of the individuality of the holocephalians.
C. The Actions of Neurohypophysial Principles in the Holocephalians
There is no direct evidence concerning the actions of neurohypophysial principles in the holocephalians. The most that can be suggested is
that the apparent anatomical existence of a hypophysial portal system
may indicate a local control of the adenohypophysis, while direct neural
connections to the pars intermedia may suggest that there is a control of
the intermedia cells. The direct drainage of the neurointermediate lobe
sinuses into the general circulation is compatible with possible systemic
functions of the holocephalian neurohypophysial principles.
V. BONY FISH: THE BRACHIOPTERYGIANS
A. The Structure of the Neurohypophysis of the Brachiopterygians
The correct classification of the brachiopterygians (or polypterine)
bony fish is disputed, but it is likely that they are the closest living relatives
to the early, extinct paleoniscoid stock (Ken-, 1968), and a number of
authors have recognized primitive characteristics in their pituitaries
(e.g., Bickford, 1895; de Beer, 1926). However, most attention has been
paid to the open oro-hypophysial duct which connects the adenohypophysis to the mouth (Fig. 6 ) , and the neurohypophysial system has
145
its pharmacological spectrum. Partition chromatography did not distinguish the Hydrolagus neutral peptide from oxytocin, but in this case
multiple biological assays against oxytocin itself showed a close parallel
between the properties of the two active agents. It must be concluded
that present evidence suggests that oxytocin is the natural, neutral principle of Hydrolagus colliei, but no final decision will be possible until this
is confirmed by chemical analysis.
The presence of arginine vasotocin in Hydrolagus colliei is not a surprising finding, and the low proportion of this principle is reminiscent of
the situation in the elasmobranchs. However, the possible presence of
oxytocin in the holocephalians is a remarkable observation, since this
principle is most closely associated with the mammals and its existence
so early in the vertebrate tree is not in accordance with current theories
of neurohypophysial evolution (Acher et al., 196%). It is another example of the individuality of the holocephalians.
C. The Actions of Neurohypophysial Principles in the Holocephalians
There is no direct evidence concerning the actions of neurohypophysial principles in the holocephalians. The most that can be suggested is
that the apparent anatomical existence of a hypophysial portal system
may indicate a local control of the adenohypophysis, while direct neural
connections to the pars intermedia may suggest that there is a control of
the intermedia cells. The direct drainage of the neurointermediate lobe
sinuses into the general circulation is compatible with possible systemic
functions of the holocephalian neurohypophysial principles.
V. BONY FISH: THE BRACHIOPTERYGIANS
A. The Structure of the Neurohypophysis of the Brachiopterygians
The correct classification of the brachiopterygians (or polypterine)
bony fish is disputed, but it is likely that they are the closest living relatives
to the early, extinct paleoniscoid stock (Ken-, 1968), and a number of
authors have recognized primitive characteristics in their pituitaries
(e.g., Bickford, 1895; de Beer, 1926). However, most attention has been
paid to the open oro-hypophysial duct which connects the adenohypophysis to the mouth (Fig. 6 ) , and the neurohypophysial system has