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SUMMARY.

  • 1
     The normal reproductive cycle of the minnow, Phoxinus laevis, is described, and some environmental factors which influence it are examined.
  • 2
     A high temperature of 17° C. in winter allows the early maturation stages, started in the previous summer, to continue. Such development, however, only proceeds as far as the production of primary spermatocytes, or the early part of the secondary growth phase of the primary oocytes.
  • 3
     Long daily periods (17 hours) of artificial light in winter, together with a temperature of 17° C., induce maturation of the gonads with the formation of spermatozoa and ova. A certain critical temperature is necessary before the gonads can be stimulated to maturity.
  • 4
     In male fish subjected to extra light, together with a temperature of 17° C., the vas deferens is found to have acquired an opening into the kidney duct. In the female a comparable opening is not induced.
  • 5
     The implications of these results are examined in relation to other known types of reproductive cycles of the fish and higher vertebrates.