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COMPARATIVELY little information is available on the factors governing the size of nematode infestations in wild mammals. Elton et al.1 showed that infestations of Nematospiroides dubius in field-mice (Apodemus) tended to become larger as the host increased in weight, and Evans2 demonstrated a similar tendency for Graphidium strigosum in wild rabbits (Oryctolagus); but for Passalurus arnbiguus he found that, after rabbits reached a weight of 3½ lb., infestations declined with further increase in host-weight. The authors interpreted their results as indicating the effects of increasing age of host. Recent work on the parasites of the wild rabbit (Oryctolagus cuniculus L.) in New Zealand gives confirmation of Evans's results for G. strigosum, and provides the first adequate picture of population-size in Trichostrongylus retortaeformis, a picture which differs markedly from those of the other nematodes mentioned above and forms the subject of the present communication.

IT is well known that myxomatosis has caused a high mortality among wild rabbit populations in most parts of England and Wales, and in those parts of Scotland and Ireland to which the disease has spread. Where it has been possible to make accurate observations, a mortality-rate of about 99 per cent was found. A similar death-rate was usual in Australia during the first year (1950–51) of their epizootic, but attenuated strains were found from 1953 onwards1.

THE first successful introduction of the European wild rabbit, Oryctolagus cuniculus, into Australia took place in 1859 when two dozen animals were imported into Geelong, Victoria1. Subsequent minor introductions may have occurred but the evidence indicates that existing populations are derived mainly from the Geelong colony2. Rabbit populations now occupy varied environments across the southern two-thirds of Australia3. These rabbits provide a good opportunity for the study of evolutionary divergences.

POPULATION studies of the wild rabbit (Oryctolagus cuniculus) in New Zealand and elsewhere have emphasized the need for reliable methods of age determination. Since weight is a satisfactory criterion of the age of young rabbits up to 3–4 months, when they become sexually mature1. the sequence of epiphyseal fusion of bones was examined in an attempt to determine the age of older animals. This work was initiated by Watson and Tyndale-Biscoe2, who found that the epiphysis at the head of the tibia fused at 41 weeks (range 33–44 weeks). Further work by Tyndale-Biscoe3 (and unpublished work) showed that the epiphyses of all other long bones unite at about the same age or earlier than do those at the head of the tibia, but that the epiphyses of the vertebrae do not fuse to the centrum until later in life, and could therefore provide an age criterion for older animals.

SINCE my previous communication on this subject1various fresh data have thrown new light on the coprophagy or refection rhythm in wild rabbits. Taylor2 reported, that of a number of wild rabbits shot and examined for the presence in the stomach of soft faecal pellets such as are re-ingested immediately, those shot in the evening contained such pellets ; those shot in the morning did not. He suggested, therefore, that the rhythm in wild rabbits was the reverse of that found in domestic rabbits ; the resting period of the former being during the day, naturally this would be the time when soft or 'night' pellets are produced and swallowed.

PROFESSIONAL rabbit-catchers in Pembrokeshire, when asked what was the average number of faecal pellets dropped by the wild rabbit (Oryctolagus cuniculus L.) in 24 hr., estimated the ‘output’ to be between 20 and 50 pellets. They based their estimates of numbers of rabbits present in a warren on these figures for pellets visible on the ground; which figures had, of course, to be multiplied by the number of days during which, they believed, a faecal pellet survived above ground—about one week in wet, and several weeks in dry or frosty, weather—before it disintegrated or disappeared.

DURING investigations into the population dynamics of the European wild rabbit (Oryctolagus cuniculus L.) on the island of Skokholm, Pembrokeshire, an abnormal condition of adipose tissue was observed. The condition is apparently unknown in rabbits elsewhere, except on the adjacent island of Skomer, and is hitherto undescribed.

LITTLE reliable information is available on the breeding cycle of the wild rabbit (Oryctolagus cuniculus) in New Zealand, though there is a widely held popular belief, quoted by Marshall1, that in certain localities the animal breeds throughout the year. An investigation of the reproduction of the wild rabbit has been carried out on the Gwavas Forest area, thirty miles south-west of Napier in the Hawkes Bay Province of the North Island of New Zealand over the period March 1950–February 1952. During this time, 1,766 adult females were examined: a female having a paunched weight of more than 700 gm. was taken as adult, this being the lightest weight of any pregnant animal found.

REPORTS of recent experiments by Madsen1 and Eden2 have shown refection to be a normal physiological process in the laboratory rabbit. A few observations collected by me, while studying the ecology and population dynamics of the wild rabbit, suggest that this process also occurs in natural conditions. From Eden's experiments, 54–82 per cent of faeces passed are shown to be normally refected, the advantage of the process to the rabbit being equivalent to "chewing the cud". It is possible that there is a further ecological advantage, which operates under wild conditions.