Rotifers Are Microscopic Freshwater Organisms Commonly Called Wheel Animals

Rotifers are microscopic freshwater organisms commonly called wheel animals. This name originated because these animals have a band of cilia at their mouth end that can look like a rotating wheel. These cilia are used in locomotion, but also create a current that draws water and particulates into the organism's mouth as it feeds. Reproduction and the life cycle of these organisms can be interesting. Some species consist entirely of females. In other species, males and females can be found, but males are only found rarely and often during times of adverse environmental conditions, such as extreme heat or drying of the pond. Males do not usually possess a functional digestive system and are short-lived. They have a single testis and are often already sexually fertile at birth. Mating occurs when the male either inserts his penis into the cloaca of the female or injects sperm directly into her body cavity. Embryos develop within the female, and most species hatch as miniature versions of the adult. Developing embryos are found in the __________ of the female.

A) uterus
B) oviduct
C) urethra
D) placenta