Hermaphrodite System

The hermaphroditic reproductive system is structured to produce both sperm and eggs. The sperm fertilize the eggs internally, and additional anatomy works to lay the developing embryos.

The system is organized bilaterally into two gonadal arms. Each arm contains one copy of the gamete development and fertilization apparati and the two arms join in the middle to form one egg-laying apparatus.

Distal tip cell (DTC): A single large cell at the end of the gonadal arm. It is the first cell present in the developing reproductive system. It helps to direct the development of the system and the gametes contained therein.

Gonadal sheath: A single layer of cells covering the germ line cells in the gonadal arm. The sheath consists of five pairs of identical cells each with different roles in development. The cells envelop germ line cells and aid in spermatogenesis and oogenesis. As the germ line cells travel from the DTC to the spermatheca through the gonadal sheath they mature and fully develop.

Spermatheca: A twenty-four cell structure distal to the gonadal sheath. This is the fertilization apparatus of the worm. Mature sperm colonize the structure during development and await the entrance of oocytes. Oocytes enter one at a time and are fertilized. The spermatheca contains a valve on either end in order to control the entry and exit of oocytes into the structure. The distal valve is called the spermathecal-uterine valve (sp-ut valve)

Egg-laying apparatus (uterus, vulva, VC, HSN neurons): A structure distal to the spermathecae, which contains and nourishes developing embryos and then lays the embryos. The apparatus is made of the uterus, uterine muscles, the vulva, vulval muscles, and a neuropil made up of neurons that direct egg laying. The vulva is the reproductive tract’s opening to the external environment.

Male System

The male reproductive system is structured to produce mature sperm which are then used for the fertilization of hermaphroditic eggs.

Male worms contain a single germ line apparatus that develops germ line cells and produces spermatids, a somatic gonad that stores and transports mature sperm and accessory liquids, and a proctodeum which is a modified rectum that contains the outflow of the alimentary canal and the reproductive system. The proctodeum also contains the structures necessary for copulation.

Distal tip cells (DTC): Two large cells on the distal end of the germ line apparatus. They help to regulate the mitotic and meiotic division of germ line cells.

Germ cell apparatus: A region of the male reproductive tract where stem cells undergo mitosis and meoisis as the migrate proximally towards the somatic gonad. The worm’s spermatids form in this region. They will remain spermatids until they enter the hermaphrodite’s uterus and become spermatazoa.

Seminal vesicle: A structure distal to the germ cell apparatus that consists of an inner tube of twenty secretory cells surrounded by the cytoplasmic processes of three larger cells. The structure stores spermatids before they are ejaculated.

Vas deferens: A long secretory tube made up of thirty cells that conduct spermatids from the seminal vesicle to the cloaca for ejaculation. Cells of three distinct morphologies are present.

Cloaca (spicules, opening): An epithelial structure that joins the openings of the alimentary canal and the vas deferens to the exterior world at the end of the worm. The cloacal opening is the actual opening of the epithelial structure to the environment. Copulatory spicules are housed within the cloaca. These structures protrude from the worm, probe for the hermaphrodite vulva, and attach to the hermaphrodite during copulation.

Embryonic Development

C. elegans takes about thirteen hours to develop from zygote to larva. During this time, the first five and a half hours contain only division into more undifferentiated cells within the egg—the process of forming organs (morphogenesis) doesn’t begin until after this. Organs develop for the next six and a half to eight and a half hours, at which point the worm’s development halts unless food is available. Laying by the mother typically occurs around two and a half hours into development; hatching at around ten. The mature embryo has a well-developed nervous system and is capable of finding food on its own. At the end of embryonic development, the worm has a little over half of its total cells.

Larval Development

Once food has been found, development proceeds, and cell division resumes three hours after hatching under ideal conditions, although arrested larvae can survive 6–10 days without food. The worm progresses through four distinctive stages, termed L1–L4, which are separated from each other by molting events, in which the worm sheds its cuticle. Collectively, larval development takes forty-five to fifty hours, and ends with the laying of eggs in hermaphrodites shortly after the fifth molt. The reproductive system, somewhat neglected during embryonic development, grows substantially during the larval phase.

Dauer

If the worm determines that its environment is particularly food-poor, overcrowded, or of an unfavorable temperature, it will enter a form of hibernation called the dauer state. (There is a preface state to dauer, called L2d, in which it is still possible to revert into an L3 larva.) The worm becomes thin, develops a thick, protective cuticle, closes some of its orifices, and waits until better conditions present themselves. A worm in the dauer state does not experience a diminished adult lifespan, and will reach leave dauer within an hour of locating food, reaching L4 some nine hours later.

Adulthood

The adult hermaphrodite lives for 13 to 19 days, including 3–4 days of egg laying. The hermaphrodite only has a supply of about 300 spermatozoa, developed during L4, but can produce up to 1400 progeny over the adult lifespan if a male is available to fertilize it. Τhe hermaphrodite has 959 somatic nuclei, 302 of which are neurons and 95 are body wall muscle cells, which are multinucleated. The male has 1031 somatic nuclei. 381 of these are neurons.