The author summarizes the endocrinological aspects of reproduction in the bony and eartilaginous fishes, in the light of the most recent obsevations. The enormous number of species which constitue the superelass Pisces together with the extensive variety of modes of reproduction reader sehematization of the complex endoerine correlations most difficult. In general in may be said that the reproduective phenomena of the Pisces are coorldinated by the secretion of bormones characteristic of the vertebrates, and as in all other vertehrates, the gonads and the hypophysis play a predominant role in this regard. Other endocrine galnds, such as the thyroid and the adrenal, are certainly involved, but very little is known about these. After a description of various morphological aspects of the glands of interanl secretion that have a relationship with reproductive phenomena, the author goes on to discuss the secretions and their physiologiceal effects. The secretions of the sex hormones appear to be qualitatively identical to those of the higher vertebrtes, while from the quantitative point of view they differ with respect to the relative concentration of the various steroid extracted from the gonads. Such differences could be due, according to the author, to different relative concentrations of the enzymes involved in the biosynthesis of the sex hormones. The hypophysis of the Pisees of fundamentally similar to that of the mammals and in large part it secretes similar hormones. Numerous morphological and histophysiological studies demostrate the participation of this gland in the reproductive phenomena, wether in the oviparous, ovoviviparous or viviparous species. Experimental investigations on hypophysectomy in the viviparous species seem to exclude the existence of causal physiological relationships between the hypophysis, the ovary and the genital tract, in as much as hypophysectomy is not followed by aborition. On the other hand, the author considers it unwise to exclude such correlations completely until the morphological and histophyiological behavior of the various organs having relationshiop with reproductive phenomena have been more thoroughly studied. Relationships may exist that are yet compatible with gestation.