Diagram of Late Stages

Developmental stages of amphibians.

(Based on Rugh, 1948)

(A) Stage 17: Tail bud forms. The embryo is shown from the dorsal side. The tail begins forming. A short stubby tail bud is seen at the posterior end. (B) Stage 18: Muscular response begins. The embryo is shown in lateral view. The embryo and tail bud are elongating, and the gill plate, which will form external gills, is visible. Muscular movements have started, and the embryo can be seen to twitch within its vitelline envelope. (C) Stage 19: Heartbeat begins. The embryo continues to elongate, the gill plate is subdivided, and the heart has begun to beat. (D) Stage 20, gill circulation and hatching. The embryo hatches from its vitelline envelope, the gill plate is further subdivided, and gill circulation is evident. (E) A generalized diagram of a young tadpole, the larva of an anuran. They possess oral suckers which allow them to attach. The gills are no longer visible, being enclosed in an opercular chamber with usually only one opening to the outside. (F) A generalized diagram of a young larva of a urodele. Called simply a salamander larva, it has a pair of balancers and visible external gills, which become long and featherlike as the larva grows.