The "third eye"-- a new concept of trans-differentiation of pineal gland into median eye in amphibian tadpoles of Bufo melanostictus.

Median third eye was found to develop from transplanted pineal gland of external gill stage tadpoles in the recipient 5 toe stage tadpoles of Bufo melanostictus. Pineal gland along with a bit part of brain tissue of the donor external gill stage tadpole was cut out and transplanted into a pit made between two lateral eyes of 5 toe stage recipient tadpoles. Half of the operated tadpoles were treated with vitamin A (15 IU/ml.) for 15 days. Median "third eye" was found to develop in the both untreated and vitamin A treated tadpoles. However, vitamin A increased the percentage of the development of median eyes. Morphological and histological study revealed that newly transformed median eyes were similar to that of normal functional eyes. A stalk like structure developed which connects the median eye to the brain. The median third eye could not develop when pineal gland of 5 toe stage mature tadpole was transplanted into the tadpole of the same age.

Homeotic regeneration of eye in amphibian tadpoles and its enhancement by vitamin A.

After removal of both the lateral eyes of external gill stage tadpoles of the toad Bufo melanostictus, the pineal organ gets transformed into a median eye. This type of transformation occurs in tadpoles of both control and vitamin A treated groups. However, vitamin A increases the likelihood of homeotic regeneration (57% in the control group and 71% in the vitamin A treated group). Histological studies showed that the newly transformed median eye developed from the pineal organ. The pineal eye so developed possessed all components of a normal eye such as a retina, sensory cells and lens.