Perineal glands are situated -

Correct Answer: C

Rationale: The correct answer is C: Below the tail. Perineal glands are located in the perineal region, which is the area between the anus and the external genitalia. This location is below the tail in animals. Choice A is incorrect because perineal glands are not situated in the rectum. Choice B is incorrect as perineal glands are not near mammary glands. Choice D is incorrect as perineal glands are not located in the subcutaneous fat layer. Therefore, the correct location of perineal glands is below the tail.

Correct Answer: B

Rationale: Step 1: Arrector pili muscles are responsible for hair erection. Step 2: Sympathetic nervous system controls arrector pili muscles. Step 3: Adrenaline is released in response to stress, cold, heat, or anger. Step 4: Adrenaline activates sympathetic nervous system. Step 5: Sympathetic stimulation causes contraction of arrector pili muscles, leading to hair erection. Therefore, the correct answer is B: Adrenaline and sympathetic stimulation. Summary: - A: Adrenaline alone is not sufficient as it needs to activate the sympathetic nervous system. - C: Sympathetic stimulation alone does not explain the role of adrenaline. - D: Calcitiotinin is not involved in the contraction of arrector pili muscles.

Correct Answer: D

Rationale: The correct answer is D because the integument of a rabbit serves multiple functions. It conserves heat in winter by providing insulation, loses excess heat during summer through mechanisms like vasodilation, and regulates body temperature by adjusting blood flow and fur density. Choice A is correct but incomplete, as the integument also helps in thermoregulation. Choice B is incorrect as the integument helps in both heat conservation and dissipation. Choice C is also incorrect as the integument does more than just regulating body temperature, such as protecting against external factors and providing sensory functions.

Correct Answer: B

Rationale: The correct answer is B: Keratin. Keratin is a fibrous structural protein found in the horns, nails, hairs, and feathers of birds. It provides strength and flexibility to these structures. Collagen (A) is a different protein found in connective tissues. Mucin (C) is a glycoprotein found in mucus. Cuticle (D) is a protective outer layer found in plants and insects, not in the mentioned structures. Therefore, based on the composition and function of horns, nails, hairs, and feathers, keratin is the most appropriate choice.

Correct Answer: B

Rationale: The correct answer is B: Root of the hair. Huxley's layer is a layer of cells located in the outer root sheath of the hair follicle. It is named after Thomas Huxley, a renowned biologist. This layer plays a role in the formation and growth of the hair. The other choices are incorrect because Huxley's layer specifically refers to a layer found in the root of the hair, not in the shaft or wall of the hair follicle. Choice D is incorrect as it denies the existence of Huxley's layer in any part of the hair structure.