Further observations on the territorial function and histology of the submandibular cutaneous (chin) glands in the rabbit, Oryctolagus cuniculus (L.)

Chinning—the deposition of secretion of the submandibular glands—is described and its role in the territorial marking of the free living Australian wild rabbits, Oryctolagus cuniculus (L.), is emphasized. The frequency of chinning and the weight and histology of the submandibular glands of a large number of free-living wild rabbits and of domestic rabbits have been studied experimentally. A small number of chin glands from hares, Lepus europaeus P. have been studied for comparative purposes. The chin glands are larger in males than in females. Sexual dimorphism appears when sexual maturity occurs. Males chin more frequently than females. The size of the gland and the frequency of chinning are correlated with social status. The glands seemed to be largest and most active during the breeding season. Castration during early life inhibited both the development of the glands and chinning in male rabbits, but in castrated females the size of the gland actually increased as compared with non-castrated animals. Histological changes connected with the secretion were studied in rabbits of different ages, of different social status, of known frequency of chinning, in castrated animals, and during the breeding and non-breeding seasons. Vacuolated secretory cells were found to be associated with heavy secretion. They were not seen in immature animals or those which did not chin frequently. In some heavily secreting animals they formed the entire glandular tissue. The vacuolated cells seemed to be secretory cells in a state of intense secretion. Dark cells were more common in males. Chin glands in hares were much smaller than those in rabbits. The vacuolated type of cells was not seen in hares.