The wall consists of 9 sets of triplet fiber arranged in a characteristic pattern. Sometime before pachytene an immature centriole, or procentriole as it will be called, appears next to each of the mature centrioles.The procentriole resembles a mature centriole in most respects except length: it is more annular than
tubular. The daughter procentriole lies with its axis perpendicular to that of its parent. It
presumably grows to full size during the late prophase, although the maturation stages
have not been observed with the electron microscope. It is suggested that centrioles possess
a constant polarization. The distal end forms the flagellum or other centriole products,
while the proximal end represents the procentriole and is concerned with replication. The
four centrioles of prophase (two parents and two daughters) are distributed by the two
meiotic divisions to the four typical spermatids, in which they function as the basal bodies
of the flagella. Atypical spermatocytes at first contain two normal centrioles. Each of these
becomes surrounded by a cluster of procentrioles, which progressively elongate during the
late prophase. After two aberrant meiotic divisions the centriole clusters give rise to the
basal bodies of the multiflagellate sperm. These facts are discussed in the light of the theory,
first proposed by Pollister, that the supernumerary centrioles in the atypical cells are derived from the centromeres of degenerating chromosomes.
Spermatogenesis in the Prosobranch snails has
attracted attention since von Siebold's (45) discovery of sperm dimorphism in the European
snail, Viviparus (Paludina) viviparus (L). In Viviparus
the testis produces not only typical "hair-shaped"
sperm similar to those of other gastropods, but
also atypical "worm-shaped" sperm bearing
multiple flagella. The atypical sperm are a regular
feature of spermatogenesis in the sense that they
are formed in enormous numbers by all male
specimens, but it is unlikely that they ever fertilize
eggs (18, 36). Atypical sperm are probably found
in all Prosobranchia except the Archaeogastropoda
(3, 33). Although the mature atypical sperm of
various species differ greatly in size and appearance, their development follows a common pattern. Ankel (3) stressed this point in his study of
Janthina, a marine snail, which possesses what is
perhaps the most bizarre sperm in the whole
animal kingdom.
The first accurate account of atypical spermatogenesis was given by Meves (28) who made a
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