Embryology   Biology 441   Spring 2013   Albert Harris   Metamorphosis   Tadpole ----> Frog or toad Caterpillar ----> ----> ----> Butterfly, or moth Maggot ----> ----> ----> fly Pluteus ----> Sea urchin Sea Squirt "tadpole" ----> Sea Squirt A dozen or more other examples among animals Trochophore larvae, Pilidium larva, and several other plankton. Ammocoetes larvae of lampreys (which are vertebrates) Larvae of barnacles look like shrimp, etc. Sponges have a swimming larval form, whose cells then rearrange to form a sponge. (in which cells keep on rearranging forever) *********************************************** In amphibian metamorphosis, stimulation and coordination by the hormone thyroxine (The same chemical higher vertebrates use as a metabolic hormone) Many parts of body change; not just loss of tail. Develop legs Also eye pigments, new optic nerve fibers, eyes move to front of head. Intestine shortens. Gills lost. Lungs develop Change nitrogen waste products. Changes in skeleton All these changes are specific responses by the different tissues. For example, a tail grafted to some other location will still degenerate. & an extra eye grafted to the tail will NOT degenerate. Tadpole tails cut off and cultured by themselves will degenerate if thyroxine is put in their culture media.

 

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