VI. The Reproductive processes of certain mammals. Part VI. - The reproductive cycle of the female hedgehog

Abstract
The hedgehog ( Erinaceus europceus ) is a common British and North European mammal, but no thorough investigation appears to have been made of the reproductive cycle of the female. The present account is designed to fill this gap and as a contribution to the comparative physiology of reproduction. Ecological data are not included. Hubrecht (1889), working at Utrecht on the embryology of the hedgehog, gives the breeding season as June to August and the number of foetuses as 4-8. He regards the hedgehog as a primitive type. Millais (1904) states that the hedgehog breeds twice a year in Great Britain, having its first litter in May or June and its second in August or September, the period of gestation being not more than one month. Five to seven young are born, which are blind at birth ; after about three weeks their spines harden and they assume adult coloration. The young are three-quarters grown by the time winter sets in. Barrett-Hamilton (1911) states that the earliest hedgehog pregnancies occur in April, but he does not include any records. Second litters are found between the middle of August and the end of September ; a late pregnancy is recorded on September 23 in Ireland and an early post-partum animal on September 28 in Scotland. There are generally four or five young, though they may vary in number from 2-9. The length of gestation is given as 4-7 weeks, but as most probably seven weeks on the authority of Lilljeborg (1874). Like Millais, Barrett-Hamilton states that the young are well grown in the same season. Both these writers describe the hedgehog as hibernating from late in November onwards ; the length and extent of hibernation are very variable, however, and the animal is not infrequently found walking about in the winter. In view of the restricted breeding season it seemed likely that the reproductive organs of the female, no less than of the male hedgehog (Marshall, 1911), would show marked changes between the anoestrous and breeding season conditions.

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