Glands of vertebrates are originated from:
a) Ectodermal
b) Endodermal
c) Mesodermal
d) All of the above

Correct answer is option 'D'

Explanation:
The glands of vertebrates are derived from all three germ layers - ectoderm, endoderm, and mesoderm. Each germ layer gives rise to specific types of glands in the body.

1. Ectodermal Glands:
Ectoderm is the outermost germ layer, and it gives rise to various glands in the body, such as:
- Sweat glands: These glands are involved in thermoregulation and secrete sweat to cool down the body.
- Mammary glands: These glands are responsible for producing milk in female mammals to nourish their young ones.
- Sebaceous glands: These glands produce sebum, which helps in lubricating the skin and hair.

2. Endodermal Glands:
Endoderm is the innermost germ layer, and it gives rise to glands in the digestive and respiratory systems, such as:
- Salivary glands: These glands secrete saliva, which contains enzymes that aid in digestion.
- Pancreas: It is a glandular organ that produces digestive enzymes and hormones, such as insulin and glucagon.
- Liver: Although not strictly a gland, the liver has glandular functions. It produces bile, which aids in digestion and detoxification.

3. Mesodermal Glands:
Mesoderm is the middle germ layer, and it gives rise to various glands in the body, such as:
- Adrenal glands: These glands produce hormones like adrenaline and cortisol, which are involved in the body's stress response.
- Kidneys: Although primarily excretory organs, the kidneys also produce hormones, such as erythropoietin, which stimulates red blood cell production.
- Gonads: The reproductive glands (testes in males and ovaries in females) are derived from the mesoderm and produce sex hormones.

In conclusion, the glands of vertebrates are derived from all three germ layers - ectoderm, endoderm, and mesoderm. Each germ layer gives rise to specific types of glands in the body, contributing to the overall physiological functions of vertebrates.