Biology Reference
In-Depth Information
Figure 10.
(1) Light micrograph of a portion of the nephric fold in a stage 1 metamorphosing
P.
marinus
showing rod-shaped clusters of neprhogenic cells (N) extending from their proximal
point of attachment with the peritoneum (P) towards the archinephric duct (A). X200. b.
Electron micrograph of nephrogenic cells at stage 1 separated by wide intercellular spaces
(I). They possess only a small amount of cytoplasm (arrows) and many are in mitosis (MF).
X 6,000. (From Youson, 1984).
(Youson, 1982). A pair of pronephric kidneys persist throughout the life
cycle of lampreys in various forms but the trend is for gradual regression
in structure and function of renal activity throughout larval life (Ellis and
Youson, 1990). The changes in the pronephroi during the seven stages
of metamorphosis have been described and relate to the fact that they
become encased within the pericardium with the development of the adult
pericardial cartilage (Ellis, 1993).
2.8.1.3 Digestive system
Past reviews of the digestive system during metamorphosis (Youson, 1980)
and throughout the life cycle (Youson, 1981a, 1981c, 1985) have emphasized
the complex set of changes that occur in the alimentary canal and liver.
There have been further studies of these organs since these earlier reviews
and we will provide a short summary of the fi ndings.
