web contact: pietsch@indiana.edu.
Here's a salamander, known as an axolotl, with the entire head of another
axolotl sticking out of its right eye socket.
The grafted head, which had been transplanted from an embryo, developed normally with two anatomically
perfect eyes and a snapping set of jaws. The transplanted head could actually
grab onto a worm, but couldn't swallow it because it lacked the rest of
its feeding equipment. The host was a larva at the time of the operation, and it went on to live for several months after this picture. The graft remained healthy too.
Actually, the operation had a very mundane original purpose. I wanted to get radioactive isotopes into the embryonic cells that eventually make the eye muscles of the donor; that would have involved injections, several per individual, which the delicate, yolk-ladened belly of the embryo wouldn't have tolerated. Instead, I thought, I'll graft embryonic heads to larvae before the eye muscle forms; then after the donor takes, I'll just inject the stuff into the host's abdominal cavity, whose tissues are much more rugged than the embryo's.
In theory, the idea seemed fine. Practice was something else. The isotope experiments called for lots of cases. But only a small percentage of the few dozen pilot operations yielded intact heads. In most, the embryonic head, while it took, sustained major damage before the eye socket developed; most results were nothing like the specimen in the picture, to say the least. To get the required numbers, I estimated, I'd need more animals than exist in the stock of the Indiana University Axolotl Colony.
Did the two heads end up housing a single mind? I tried to find out with a variety of visually cued tests; reflected images of wriggling worms, for example. But targets confined to the visual field of one head would not make the eyes of the other head respond. By all indications, and as neat as it might have been otherwise (to me) and as intimately connected as the two heads were, each retained its separate psychological identity, throughout. The two heads weren't really better than one.