REPRODUCTION IN THE ORKNEY VOLE (MICROTUS ORCADENSIS), UNDER A SIX‐HOUR DAY‐LENGTH AND OTHER CONDITIONS

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Abstract
SUMMARY: There is no significant difference between the reproduction rates of laboratory populations of Orkney Island Voles (Microtus orcadensis) existing under (a) winter day‐length (six hours) and (b) London summer day‐lengths (fifteen hours to fifteen hours twenty‐eight minutes) if abundant food is provided at ordinary such summer temperatures. These data, and other considerations discussed, suggest that, as in birds, environmental factors other than photoperiodicity alone, probably govern the sexual cycle of some mammals. A grouped arrangement of interstitial cells essentially similar to that occurring in birds is described. As spermatogenesis proceeds these cells expend their cholesterol‐positive lipids as do those of birds. The seminiferous tubules do not undergo a post‐nuptial metamorphosis. Even when males are kept alone in total darkness the germ‐cells retain their integrity and do not metamorphose as do those of passerine birds under semidark conditions.

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