|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 6. Elongation of the leech body plan from teleoblasts. (A) The
teleoblasts of the leech (annelid) embryo produce elongating germinal bandlets
through the sequential production of blast cells by highly unequal divisions.
On each side, four ectodermal bandlets (N, O/P and Q) come into lateral
apposition, while the mesodermal (M) bandlet comes into apposition from
beneath. The five bandlets form the germinal band, which extends across the
embryo (arrow, A) as bandlet cells are added posteriorly by highly unequal
cell divisions of the parent teloblasts. The germinal bands anneal with their
contralateral partner in a rostrocaudal sequence at the midline to form the
germinal plate. (B,C) As the germinal bandlets extend by cell
division and anneal, they, and the micromere cap overlying them, expand over
the surface of the embryo in epiboly (B, curved arrows, early stage 8, animal
view; C, late stage 8, rostral view). (A) Reproduced, with permission, from
Nelson and Weisblat (Nelson and Weisblat,
1991); (B,C) reproduced, with permission, from Smith et al.
(Smith et al., 1996).
Asterisks indicate apposition of germinal bands.
|
