The Biological Basis of Sexual Behaviour in Amphibia

1. The complete disappearance of all sexual activity in Xenopus laevis, male or female, is observed under laboratory conditions. 2. A technique is described whereby the mating reflex (coupling) can be established in the laboratory during the pond breeding season as well as midway between breeding seasons, by means of injections of human pregnancy urine extracts, or by acid extracts of the anterior lobe of the pituitary gland of sheep and goats. 3. The mating reflex has been induced in 101 different pairs of toads with pregnancy urine extracts and in 39 different pairs of toads with anterior pituitary extracts. 4. The reflex induced by anterior pituitary extracts in no way differs from that produced by pregnancy urine extracts. 5. The possibility that the extract acts through the intermediation of the gonads is considered. 6. The mating reflex is described, and attention is drawn to the passive role of the female, while the male is stimulated to activity. 7. It is suggested that a stimulus from the female reflexly activates the male to clasping activity. 8. Fertilised ova from coupling pairs have been reared successfully to an advanced tadpole stage (4-5 months). Tadpoles can be reared also midway between breeding seasons. 9. The injected extract, acting possibly through the intermediation of the gonads, may be suggested to inhibit the clasping reflex inhibitory centre in the brain described by Steinach and others. 10. The mating reflex appears to be independent of the pituitary mechanism associated with chromatic response in Xenopus laevis. 11. The larger doses (500 mg. fresh tissue) of anterior pituitary extract required to produce in summer a response of the same magnitude as that produced by smaller doses (192 mg. fresh tissue) in winter cannot be attributed to a diminished sensitivity of the ovaries. 12. Control extracts of male urine and of sheep and goat brains repeatedly gave negative results.