188
A. M. PERKS
injection of doses as low as 2.5 nglkg of arginine vasotocin into Protopterns aethiopicus resulted in sharp increases in the blood pressure in the
dorsal aorta. However, the pressor response was outlasted by the increase
in glomerular filtration rate, so that it was unlikely that the increased
filtration was totally dependent on a raised systemic blood pressure.
Nevertheless, it is possible that more subtle effects on the glomerular
arterioles might persist after the gross change of aortic blood pressure.
There is no information concerning the role of the neurohypophysial
principles in the control of the pars intermedia or of the adenohypophysis
of the lungfish; all that can be said is that the anatomical relationships
are suggestive of a close association. There is no information on the possible effects of the principles on reproduction. It is tempting to speculate
that the neutral peptides of the Dipnoi could be important in this sphere;
as W. H. Sawyer (1966b) has pointed out, they are stored in greater
quantities than arginine vasotocin, but their functions are as mysterious
as those of neutral principles in the nonmammalian tetrapods and in the
male mammals.
X. CONCLUSION
Many of the data presented above are summarized in Tables I1 and
111. However, these tables are no substitute for the facts presented in the
review, since the observations listed vary from well-established facts to
solitary, and often brief, comments. It is dangerous to try to generalize
in a group as varied as the fish. Indeed, there are more variations, both
fundamental and individual, between the different classes and species of
fish than exist throughout the : :urohypophyses of the tetrapods. However, a few generalizations may be useful, and they will undoubtedly
provide a rich field for future critics.
The complete neurohypophysial system exists from the cyclostomes
up through the vertebrate scale. Presumably, its primitive origins are lost
in extinct species. In the hagfish it is indistinct, and in both the hagfish
and the lampreys the pars nervosa, although present, appears to be poorly
developed. The pars nervosa becomes more marked as one progresses to
more advanced groups of fish. Above the evolutionary level of the cyclostomes, the pars nervosa becomes closely intermingled with the pars
intermedia, although the degree of this association may be somewhat
reduced in some species (e.g., Squalus acanthias) , This notable fusion
between the neural and intermediate elements persists into the lungfish,
even though the Dipnoi develop the more localized, dorsal pars nervosa
A. M. PERKS
injection of doses as low as 2.5 nglkg of arginine vasotocin into Protopterns aethiopicus resulted in sharp increases in the blood pressure in the
dorsal aorta. However, the pressor response was outlasted by the increase
in glomerular filtration rate, so that it was unlikely that the increased
filtration was totally dependent on a raised systemic blood pressure.
Nevertheless, it is possible that more subtle effects on the glomerular
arterioles might persist after the gross change of aortic blood pressure.
There is no information concerning the role of the neurohypophysial
principles in the control of the pars intermedia or of the adenohypophysis
of the lungfish; all that can be said is that the anatomical relationships
are suggestive of a close association. There is no information on the possible effects of the principles on reproduction. It is tempting to speculate
that the neutral peptides of the Dipnoi could be important in this sphere;
as W. H. Sawyer (1966b) has pointed out, they are stored in greater
quantities than arginine vasotocin, but their functions are as mysterious
as those of neutral principles in the nonmammalian tetrapods and in the
male mammals.
X. CONCLUSION
Many of the data presented above are summarized in Tables I1 and
111. However, these tables are no substitute for the facts presented in the
review, since the observations listed vary from well-established facts to
solitary, and often brief, comments. It is dangerous to try to generalize
in a group as varied as the fish. Indeed, there are more variations, both
fundamental and individual, between the different classes and species of
fish than exist throughout the : :urohypophyses of the tetrapods. However, a few generalizations may be useful, and they will undoubtedly
provide a rich field for future critics.
The complete neurohypophysial system exists from the cyclostomes
up through the vertebrate scale. Presumably, its primitive origins are lost
in extinct species. In the hagfish it is indistinct, and in both the hagfish
and the lampreys the pars nervosa, although present, appears to be poorly
developed. The pars nervosa becomes more marked as one progresses to
more advanced groups of fish. Above the evolutionary level of the cyclostomes, the pars nervosa becomes closely intermingled with the pars
intermedia, although the degree of this association may be somewhat
reduced in some species (e.g., Squalus acanthias) , This notable fusion
between the neural and intermediate elements persists into the lungfish,
even though the Dipnoi develop the more localized, dorsal pars nervosa