Biology · Structural Organisation in Animals · NEET
The whole body is segmented (metameric). The head is formed by the fusion of 6 segments. The thorax has 3 segments (prothorax, mesothorax, metathorax). The abdomen has 10 segments. For NEET, the most-asked number is that the abdomen has 10 segments in both male and female.
Yes. Like all insects, the cockroach body has three distinct regions (tagmata): head, thorax and abdomen. This three-part plan is a key feature of class Insecta and separates insects from other arthropods.
The body is covered by a hard chitinous exoskeleton called the cuticle, made of overlapping plates. Dorsal plates are called terga (tergites), ventral plates are sterna (sternites), and lateral plates are pleura (pleurites). The exoskeleton gives protection and support, and the joints between plates allow movement.
The cockroach is bilaterally symmetrical, triploblastic (three germ layers), segmented and coelomate. This matches phylum Arthropoda. These four words are commonly tested, so memorise them together.
The head bears one pair of antennae (long, thread-like sensory organs) and one pair of large kidney-shaped compound eyes. The thorax bears three pairs of walking legs (one pair per thoracic segment) and two pairs of wings.
The cockroach chapter was rationalised out of the current NCERT reprint, but it is still officially part of the NEET syllabus. NEET has asked around 15 questions on cockroach over the years, so you must still learn its external morphology from these notes.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Periplaneta americana, the American cockroach. It belongs to phylum Arthropoda, class Insecta.
The body is bright reddish-brown to dark brown, long, flattened dorsoventrally, and segmented, usually 34 to 53 mm long. The flat shape helps it squeeze into narrow cracks.
They are the hard exoskeletal plates on each segment. Terga are the dorsal (upper) plates, sterna are the ventral (lower) plates, and pleura are the lateral (side) plates. They are joined by a thin flexible cuticle that allows movement.
The head is formed by the fusion of 6 segments and shows great mobility on a flexible neck. It is triangular and lies at right angles to the body, a condition called hypognathous.
The thorax has three segments - prothorax, mesothorax and metathorax. Each segment carries one pair of legs, so three pairs in total. The mesothorax and metathorax each carry one pair of wings.
