Pronephric development of few osteichthyans
has been examined, and the available
data are crucial to consideration of relationships.
Fraser (‘27) rigorously analyzed kidney
development in the sturgeon Acipenser
and Maschowzeff (‘34-’35) examined Salmo,
as well as the sturgeon, a frog, and a salamander.
Fraser (‘27) also carefully compared
development among fishes and amphibians.
She found that Acipenser has six nephrostomic
units in the pronephros, derived from
somites four through nine. This pattern also
occurs in Salmo; it has three functional pronephric
units which must be assumed to be
the primitive actinopterygian condition. It
seems logical that the pronephric units arise
from the anterior-most body segments as a
property of cephalized development. Fraser
(’27) summarized her own work and the literature,
with the following conclusions:
1. The pronephric chamber is segmented
early on in cyclostomes, Polypterus, and gymnophione
amphibians, but slightly later in
chondrosteans (her “ganoids”) and dipnoans.
The pronephric chamber is recognizable as
segmental only in terms of numbers of tubules
in anurans and urodeles and is a single,
never metameric chamber in teleosts.
2. In gymnophiones the pronephric nephrostomal
units remain serial; in cyclostomes,
chrondrosteans, Polypterus, and dipnoans
the walls of the units break down, a
limited occurrence in anurans and urodeles.
3. In cyclostomes, Polypterus, amphibians,
and dipnoans the units open into the coelomic
space; in chondrosteans only anterior
units are open (the units of dipnoans close
developmentally like those of chondrosteans);
and the pronephric units of teleosts are
closed off from the coelom. Goodrich (’30) also
presented a useful summary of pronephric
development. Polypterus (Kerr, ’02) has two
functional tubules, Lepisosteus three, Amia
(Jungersten, 1900) three or four. The number
varies among teleosts and includes retention
of a functional pronephros in adults of some
species. Elasmobranchs have three to seven
functional units (Goodrich, ’