Of particular interest is the potential for modulation of myometrial activity associated with viviparity and the retention of developing young. In this paper we will present the results of recent studies in which we demonstrate that homologous Squalus relaxin produces a marked slowing of the spontaneous rhythmic contraction of the oviduct accompanied by a marked lengthening of the interval between contractions. In estrogen treated animals, these effects of relaxin are accentuated. In contrast, if progesterone is administered along with estradiol the effects of relaxin are not seen. These results are discussed in the context of the overall control to the myometrium of the dogfish.
Females are larger than males.
Gestation spreads about 4 to 5 months at a minimum, but it is impossible to know the number of reproductive cycles per year, vitellogenesis completes at the end of the gestation. Parturition and ovulation occur in June. The females of many species of sharks travel to specific, geographically discrete, nursery areas to lay their eggs or to give birth to their young. These nurseries are usually in shallow, coastal waters in highly productive zones, where the young find abundant prey and where they are free from predation by larger sharks. The newborn young remain in the nurseries for a few months in temperate latitudes or for a few years in tropical waters.