Somite development is a unique and important topic; unique because
somitic mesoderm is the first tissue to become segmented, important
because the somites - once established - exert a profound influence on
other seg- mental structures which form later. Somite development is of
interest at a number of levels. In one aspect, demarcation of a specific
number of somites and size regulation, it is a particularly intriguing
example of embryonic pattern formation, 'especially in vew of its
possible relation to homoeobox-controlled segmentation in insects. At
another level, somite development has long been studied by compara- tive
anatomists, but only recently has new light been thrown on such sub-
jects as segmentation of the head, proposed in the 18th century by
Goethe and now a live issue for developmental biologists. Somit es are
simple when they first appear, but very complex structures arise from
them. These include the vertebrae and the axial and other muscles and
consequently there is a wealth of morphogenetic problems to be explored.
Sometimes their morphogenesis is disturbed, by genetic or environ-
mental factors, and there are many clinical conditions which arise as a
result.