The posterior salivary gland of Octopus vulgaris is apocrine and has a discrete character in the animal kingdom. In general, studying the evolution of any toxic organism typically starts with an examination of its defense system, including the minute structures with similar organisms across various phyla in the animal kingdom. The posterior salivary gland of Octopus vulgaris consists of a thick gland wall with a contraction function for pushing the toxin through the gland duct and into the pass tube, which opens in a buccal mass. The posterior salivary gland of Octopus vulgaris secretes toxic saliva, which is thermostable liquid resistant to heat and has a darkened blue appearance when stained with bromophenol blue, more pronounced than the venom. The present gland consists of nine types of cells associated with a canal that transports the toxin from the posterior to anterior salivary glands. These glands are located in the middle of the gland and consist of a mixture of circular and longitudinal muscle fibers, respectively. The secretion of the present gland is considered analogous to the evolutionary progression from octopus to the cobra snake. In the cobra snake, there are two types of cells with thick walls that aid in the contraction of the gland to push the toxin outside the mouth. In octopuses, two small cells represent an early evolutionary stage observed in glands across the animal kingdom, as recorded in the earliest records.