Hormonal control of sex
Sex in Bonellia
In Bonellia viridis, a marine worm, all larvae are genetically and cytologically similar. In this worm, male individual lives in the uterus of the female (Fig. 17.22). If a particular larva settles near proboscis of an adult female, it becomes a male individual, and lives in the uterus of the female. On the other hand, if it has to develop free in water, it becomes a female. Similarly, if a partly developed male is detached from the proboscis it become an intersex. Obviously the proboscis secretes a substance suppressing femaleness.
A case of complete sex reversal was reported in 1923 by Crew, where a fertile female fowl (hen), which had already produced offspring, changed over to a fully fertile male (cock). This resulted due to a damaged ovary in the female. It is believed that ovary in female secreted a male suppressing hormone. Therefore, in absence of ovary, testis could develop.
The Free-Martin
Incattle, when twins are produced, one of them being male and other female, female is sterile and male is normal. These are known as Free-Martin after the name of the worker, and would be produced only when there is a vascular connection between two embryos. The hormone perhaps suppresses the development of ovary in female.