Sex Development in Parabiotic Chains of the California Newt. ∗

Abstract

In a previous communication 1 it has been shown that in parabiotic twins of Triturus torosus the heterosexual combinations give evidence of an intense antagonism resulting in the decrease of the number of germ cells in both testes and ovaries. In some cases the ovaries were found completely sterile and often they showed a tendency toward sex reversal (free-martin effect).

In an attempt to modify this experiment in its quantitative component, parabiotic chains have been made by grafting one embryo with its front end on to the tail bud of another embryo. Similar chains of 3 and 4 individuals lived up to 2 months, though only chains of 2 developed and metamorphosed at the same pace as the single controls. About 50 of these chains have been raised. A few, now over one year old, are still alive. Over half of them have been cut in serial sections.

There is some variation in the mode of union of these chains. As a rule the first animal ends at the pelvic region, where the second one is broadly attached with the midbrain region of its head. The spinal cord of the first and the brain of the second animal are grown together in most cases. Despite this very intimate fusion the larger bloodvessels have never been found connected. The two circulatory systems are linked through capillaries only.

The sexes, as expected, are found in 4 combinations. (1) In case both animals are females, the first one has without exception, the better developed ovaries, with larger ovocytes. (2) If both are males, a corresponding difference in size is even more pronounced. One may suspect this difference as being due to better nutritional conditions in the first animal.