Mesoderm-derived: Cardiovascular System; Somites; Limb Formation
Ectoderm-derived: Nervous System; Neural Crest
Stage of Development: Embryo
This is a Stage 7-8 embryo of Anolis carolinensis, or the green anole lizard. The most distinguishing feature of this stage is the paddle-shaped limb buds. The forelimbs (fl) and hindlimbs (hl) will develop digit condensations and limb joints segmenting the proximal and distal portions of the limb. Only slight digital condensations of the hindlimb (hl) are visible at this stage. The vascular system (in red) is rapidly expanding providing nutrients to growing organs and tissue. Somites (s) are becoming vascularized. There are 1-2 complete coils of the tail. The presomitic mesoderm will become exhausted and the generation of somites will cease (after 10-20 more somites form). Apoptosis of progenitor cells in the tailbud (tb) might also contribute to the termination of somitogenesis, as the embryo reaches its species-specific number of somites.
Pigment in the eye is diffuse around the iris (ir) and retina. The lens (l) is distinct and bulges out laterally. The mesencephalon (me) has expanded and is beginning to separate into lateral chambers. The mesencephalon will begin to shrink in Stage 8-9. The diencephalon (di) located between the eyes has increased in size from Stage 6.
Gomez, C., Pourquie, O. Developmental Control of Segment Numbers in vertebrates. Journal of Experimental Zoology. Mol. Dev. Evol., 2009, 314:533-544.
Sanger, T.J., Losos, J.B., Gibson-Brown, J.J. A developmental staging series for the lizard genus Anolis: A new system for the integration of evolution, development, and ecology. Journal of Morphology, 2008, 269:129-137.