Absence of Male Reproductive Organs in Two Hermaphrodite Molluscs

In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
In addition to sexual development, the X chromosome has genes involved in autosomal functions such as brain development and the immune system. Therefore, males and females with  distinct numbers of X chromosomes will have...

Development of the reproductive organs in an embryo starts from a bipotential state. This means the early embryo can develop either male or female reproductive organs. The formation of these organs begins with the growth of gonadal ridges that arise from the intermediate mesoderm during the fifth week of development.
Near the gonadal ridges, two duct systems are present: the mesonephric ducts (Wolffian ducts) and paramesonephric ducts (Müllerian ducts). These ducts form the basis for the male...

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...

The accessory ducts involved in sperm maturation and transportation include the epididymides, vasa deferentia, ejaculatory ducts, and urethra. These ducts play a critical role in the maturation, storage, and transportation of sperm from the testes to the urethra, where it is then released during ejaculation.
The epididymis is a small, comma-shaped organ located at the back of each testicle. The epididymis can be divided into three main parts: the head, body, and tail. The head of the epididymis...

The Y chromosome is a sex chromosome found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human males have one X chromosome and one Y chromosome. In these organisms, the presence or absence of the Y chromosome determines the development of male traits.
Evolution
Around 300 million years ago, the two sex chromosomes diverged from two identical autosomal chromosomes. Over time, the Y chromosome has lost most of its genes, shrinking in size. Today,...

The vulva encompasses the external structures of the female reproductive system. At the forefront is the monpubis, a cushion of fatty tissue atop the pubic bone. Once puberty sets in, this area typically grows hair. Extending from just behind the mons pubis are the labia majora (labia = 'lips'; majora = 'larger'), which are larger skin fs olds coated with hair. Nestled within are the labia minora (labia = 'lips'; minora = 'smaller'), which are thinner, more pigmented, and hairless. While the...