Examinations...

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How earthworms reproduct?

Earthworms are hermaphrodites (both female and male organs within the same individual). They have testes, seminal vesicles and male pores which produce, store and release the sperm, and ovaries and ovipores. However, most also have one or more pairs of spermathecae (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. Some species use external spermatophores for transfer instead. Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The cocoon, or egg case, is secreted by the clitellum, the external glandular band which is near the front of the worm, but behind the spermathecae. Some indefinite time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for a lack of the sexual structures, which develop later, namely, in about 60 to 90 days. They attain full size in about one year. Some earthworm species are mostly parthenogenetic.

Chapter 6 Exercise 10

Regarding to the question you guys asked about Iron filling, actually the iron filling is just the powder of iron. It put it there to react with the air when it heated up, that's why the answer is C the final iron product mixed with oxygen and become iron dioxide. Any other questions feel free to ask and post in comments, thank you.