Salivary glands are absent in

The correct option is Rana hexadactyla.

Salivary glands are specialized exocrine glands that produce and secrete saliva, which contains digestive enzymes like amylase to initiate the breakdown of food in the oral cavity. Let us examine the presence of salivary glands in the given organisms to understand why they are absent in Rana hexadactyla:

1. Musca domestica (Housefly): Houseflies possess well-developed salivary glands. Since they feed on liquid or semi-liquid food, they secrete saliva onto solid food to dissolve it before sucking it up through their proboscis.
2. Blatta orientalis (Oriental cockroach): Cockroaches have a pair of prominent, bilobed salivary glands located in the thorax region, which play a crucial role in initial food lubrication and digestion.
3. Anopheles maculipennis (Mosquito): Mosquitoes have well-differentiated salivary glands. Their saliva contains anticoagulants and other proteins that facilitate blood-feeding.
4. Rana hexadactyla (Green pond frog): Frogs are amphibians. True multicellular salivary glands are completely absent in frogs. Instead, they have simple mucus-secreting glands in their mouth (oral cavity) that serve only to lubricate the food for swallowing rather than producing digestive saliva. Furthermore, frogs swallow their prey (typically insects) whole without mastication (chewing), meaning there is no need for chemical digestion to begin in the mouth.

Therefore, salivary glands are absent in Rana hexadactyla.