THESIS APPROVAL

1.5 Reproduction
Asexual reproduction is widespread among freshwater oligochaetes.
Asexual methods vary including fission by architomy or fragmentation, and more
commonly, paratomy or formation of buds followed by fragmentation (Smith, 2001).
In paratomy method, the budding segment grows and undergoes repeated
transverse divisions that result in four or more anterior segments of a new posterior
worm and several new posterior segments of the anterior parent worm. These regions
rapidly become differentiated. The two animals remain attached for a variable length
of time, and the more posterior individual may in turn produce a third individual
posterior to its budding zone (Figure 4). This process may be repeated, so that in
some species there may be chains of as many as four to eight zooids in various stages
of development. After an interval, two adjacent and mature zooids separate and
become completely independent individuals. This regeneration has been found in
most Naididae, which is often reproduced a new individual every 2 or 3 days (Smith,
2001).
A similar ability to reproduce by fission or architomy appears to be best
developed in the Tubificidae and Naididae. It has been reported in Tubifex newaensis
and Branchiura sowerbyi (Brinkhurst and Jamieson, 1971). The occurrence of this
asexual reproduction in the Lumbriculidae is also well established, especially in
Lumbriculus variegatus (Cook, 1968). The strategy of this fragmentation is
constituted fission of worm into 2 parts, followed by anterior regeneration at the
caudal end, then posterior regeneration at cephalic end. The specific location of the
fission zone varies greatly form one individual to another within a species. In Nais
elinguis, the budding segment varies from 12 to 20, and in Stylaria fossularis, it varies
form 8 to 23 but is usually 18 (Smith, 2001).
Sexual reproduction certainly occurs in aquatic oligochaetes. They are all
hermaphroditic, but do not self fertilize. The epidermis in the reproductive zone of
the adult worm is modified to form a clitellum forming several kinds of secretory
12