Biology Reference
In-Depth Information
Figure 11.
Frequency distributions of blood cell area of Japanese fl ounder larvae treated with
either 100 ppb L-thyroxine or no hormone for 8 or 15 days. N, number of total cells counted.
[From Miwa and Inui, 1991, with permission].
blood islands on the yolk sack and intermediate cell mass, which is situated
between the somite and the lateral plate, and adult erythropoiesis occurs
in the kidney and the spleen (Iuchi, 1985). Hence, the hematopoietic cite
may also change during the shift of erythrocyte populations in the Japanese
fl ounder, although the origin of larval erythrocytes is not known.
4.2.5.2 Gastric development
In most fi shes, the larval alimentary canal is functional at fi rst feeding, but
is structurally and functionally less complex than that of the adults, and
pinocytosis and intracellular digestion play important roles on the digestion
of food during larval stages (for the review see Govoni et al., 1986). Many fi sh
species lack the stomach in early stages of life, and the functional stomach
develops during larva-juvenile transformation, i.e., metamorphosis (Govoni
et al., 1986). The gastric glands rapidly develop during metamorphosis
in the fl ounder (Miwa et al., 1992). In premetamorphic larvae, the wall of
the anterior portion of the foregut, which later develops into the stomach,
consists of a thin smooth muscle layer, a thin connective tissue layer and a
simple cuboidal epithelium, and no glandular structure is observed (Fig.
12-a). During metamorphosis, the epithelium forms complex folds and
