The clutch patterns of hens in constant illumination

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Abstract
1. Although flocks of hens under constant illumination lay eggs by night and day, it has not yet been demonstrated that the number of eggs laid by night is equal to the numbers expected on a hypothesis of random distribution around the clock. 2. Hens under continuous illumination lay eggs at quite regular intervals. With highly productive pullets and a limited period of observation (e.g. 10 weeks), many birds lay unbroken sequences (i.e. intervals between consecutive ovipositions do not exceed 33 h). 3. Some birds under continuous light lay eggs in clutches (i.e. one observes characteristic inter‐clutch intervals of 35 to 41 h between ovipositions). However, the first egg of a new clutch has a high probability of being laid between 05.00 h and 16.00 h and this is taken as evidence that the timing of clutches is dependent on diurnal environmental influences which persist in spite of attempts to provide a non‐varying environment. 4. The evidence available neither supports nor refutes the hypothesis that under constant environmental conditions an internal “ clock “ with a fixed period is responsible for timing the open periods during which release of luteinising hormone may occur. 5. Further experiments are needed with hens having a lower rate of lay, and therefore more likely to lay in clutches, maintained in a better‐controlled constant environment.