Hemimetabolism is a form of "incomplete" metamorphosis. Cockroaches, along with many other species, emerge from eggs as nymphs. Nymphs are very similar in physiology and morphology to an adult cockroach, therefore it's an "incomplete" metamorphosis or change. Nymph stages are called instars and each one is numbered after each molt. Ways to tell the difference between adult and nymph cockroaches are size (nymphs being smaller) and the presence of wings (nymphs do not have any). (Reference 1)
The exoskeleton is thick and made of plates called sclerites. This is very important to make sure the cockroach does not dehydrate. Through nymph stages, cockroaches will molt and shed their exoskeleton.
Cockroaches have compound eyes. They contain 2,000 ommatidia, which give them several views of one object. They are also have nocturnal vision.
(References 7, 10)
There are three main parts to the digestive system: the foregut, midgut and hindgut.
The foregut contains the gizzard, which crushes food in the first step of digestion.
The midgut is more important for enzymatic activity, to chemically digest the food.
The hindgut absorbs water and nutrients in the last stages of digestion.
Cockroaches do not have "brains" but instead have nerve bundles called ganglia. Ganglia are sensitive nerve centers. Below there is an image that shows where ganglia are centered.
Cockroaches breathe through tubes that reach every cell in the body. They are called tracheae. Tracheae are attached to spiracles. They are all located on the body, so a head is not essential for survival.