Tony Wu / Humpback whale (Megaptera novaeangliae) adult female at rest. The tubercles on the whale's head are clearly visible, as are the barnacles (Coronula diadema), whale lice (Cyamus boopis), and hairs on t...

David Fleetham / Humpback whale (Megaptera novaeangliae), close up on tubercles on underside of chin. Hawaii.

David Fleetham / Humpback whale (Megaptera novaeangliae) spyhopping, close up on tubercles on underside of chin. Hawaii.

Magnus Lundgren / Wild Wonders of China / Short-legged horned toad (Megophrys brachykolos) held in human hand, showing white tubercles, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Moth caterpillar, tubercles with urticating hairs. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Moth caterpillar on leaf, tubercles with urticating hairs. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Moth caterpillar on leaf, tubercles with urticating hairs. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Joao Burini / Close-up on the skin tubercles of a Treefrog (Scinax littoralis) with copper iridescence visible. Tapirai, Sao Paulo, Brazil. South-east Atlantic forest.

Tony Wu / Nudibranch (Cadlinella ornatissima), yellow with pink tipped tubercles and white rhinophores. Japan. March.

David Fleetham / Tubercles on the top of the head of a humpback whale (Megaptera novaeangliae), Hawaii. ^^^ Each protuberance contains at least one stiff hair whose purpose is not known, though they may provide the wh...

Tony Wu / Humpback whale (Megaptera novaeangliae) with tubercles on the whale's head clearly visible, they contain a hair follicle, and may be for used for sensory purposes, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novaeangliae) large male spyhopping in the early morning, Vava'u, Tonga, South Pacific The single hairs in the whale's tubercles are visible, as are hairs on the front of the...

Espen Bergersen / Close-up of a spyhopping Humpback whale (Megaptera novaeangliae) showing the knobs (tubercles) which are enlarged hair follicles possibly used for sensory purposes. Kvaloya, Troms, Northern Norway. No...

Espen Bergersen / Close-up of a spyhopping Humpback whale (Megaptera novaeangliae) showing the knobs (tubercles) which are enlarged hair follicles possibly used for sensory purposes. Kvaloya, Troms, Northern Norway. No...

Chris Mattison / Australian barking gecko (Underwoodisaurus milii) scales from shed skin, showing granular scales with scattered tubercles.

Mark Carwardine / Humpback whale (Megaptera novaeangliae) surfacing, showing bloodied tubercles from fighting, Sea of Cortez, Baja California, Mexico

Mark Carwardine / Humpback whale (Megaptera novaeangliae) at surface showing bloodied tubercles on head during courtship battle, Sea of Cortez, Baja California, Mexico

Steven David Miller / Humpback Whale (Megaptera novaeangliae) spyhopping near boat, Hervey Bay, Queensland, Australia

Chien Lee / Curved Spiny Spider (Gasteracantha arcuata) showing unusual tubercles with unknown function, Lambir Hills National Park, Borneo, Malaysia

Chien Lee / Curved Spiny Spider (Gasteracantha arcuata) with unusual tubercles with unknown function, Lambir Hills National Park, Borneo, Malaysia

Flip Nicklin / Humpback Whale (Megaptera novaeangliae) spyhopping showing bumps called tubercles, vulnerable, southeast Alaska

Flip Nicklin / Humpback Whale (Megaptera novaeangliae) spyhopping showing bumps called tubercles, vulnerable, southeast Alaska

Joel Sartore / Photo Ark / Tricolor shiner (Cyprinella trichroistia) male with nuptial tubercles, Goodwater, Alabama. Captive.

Brian Bevan / Minnow (Phoxinus phoxinus) group of breeding males showing tubercles, Bedfordshire, UK, May.

Brian Bevan / Minnow (Phoxinus phoxinus) breeding male showing tubercles, Bedfordshire, UK, May.

Linda Pitkin / Nudibranch (Doto ussi) on hydroid, covered in tubercles which help camouflage the animal. Lembeh Strait, North Sulawesi, Indonesia.

David Fleetham / Humpback whale (Megaptera novaeangliae) surfacing showing tubercles, Hawaii.