H.—4.

expel the whole or a portion of the tape-worms. In some animals, it is true, the presence of tapeworms is distinctly injurious—as, ior instance; the Tcenia expansa, which I have found in New Zealand on several occasions as a cause of debility in lambs. On the other hand, dogs seem to suffer less from their tape-worms, of which no fewer than eleven species are recorded, some being of very common occurrence. The natives of Abyssinia are almost without exception infested by the unarmed human tape-worm (Tc&nia mediocanellata). So far from regarding this as a cause of weakness or disease, they say that in many ways its presence exercises a beneficial influence on the health, and if they have the misfortune to lose their parasite they take measures to obtain another. 3. Value of the Liver-coccidia. Although the disease caused by the liver-coccidia does not satisfy the second of our conditions —namely, that the disease must not be injurious to man or any of the animals useful to man—it will be necessary to refer to it here, because it is a disease capable of inflicting serious injury on rabbits, and has, I believe, been operative in some degree in reducing the rabbit-pest in the Wairarapa. I have not had the opportunity of acquiring sufficiently ample data to enable me to decide to what degree it has been operative, but I found the Coccidia present in a larger percentage of rabbits than the bladder-worm. Near Masterton, out of nineteen rabbits dissected in one morning, eleven were affected by this disease, and five of them badly. I may add here evidence from other sources as to the destructiveness of the disease. A few years ago, whilst investigating the natural history of the liver-fluke for the Royal Agricultural Society of England, I paid some attention to the parasitic diseases of rabbits. The rabbits in certain localities near Oxford had, after a series of wet seasons, been greatly reduced in numbers, and were found lying about dead on the ground. Some of these were brought to me for examination. One of them proved to have been killed by the liver-fluke ; in another the; liver was extensively invaded by the-Goccidia, which had been the cause of death. Leuckart says of the liver-coccidia of the rabbit that the disease is endemic in many warrens, so that scarcely a sound rabbit is found. "As soon as the disease reaches a considerable development, the rabbits are constantly seen to perish. After passing, perhaps, a few weeks in a sickly condition, they become very thin, lose the desire to eat and their former activity, begin to breathe more quickly and violently, and die at last in convulsions." The disease has been found in man on at least four occasions ; in one case it was the cause of death. On this account the artificial encouragement of the disease could not be advocated. Nevertheless the disease has been introduced into the district, and it would be a difficult matter to stamp it out if it were desired. It seems not improbable that it will develop further, and, whether we wish it or not, may prove the cause of death to a certain proportion of rabbits. Men, however, are very seldom exposed to the risk of infection with the liver-coccidia, and that only where uncleanly habits prevail; so that the presence in the district of this disease threatens little danger to human life. 4. Possibilities of Destruction of Babbits by Parasitic Disease. Surprise is often expressed at the rapid rate of increase of rabbits in Australasia. This is not to be attributed to the greater fecundity of the rabbit here, but rather to the absence of those checks upon its naturally rapid increase which operate in keeping. down the rabbits in other parts of the world. Every living being in a state of nature is subject to an active or passive struggle for existence. It constantly endeavours to increase its kind and extend its area, whilst it meets with various adverse influences, or checks to its increase, against which it may be said to struggle. Even in Europe the rabbit sometimes increases to such an extent as to become a nuisance ; but there the checks to its increase are much greater. These checks may be grouped as follows : (1) Action of man; (2) scarcity of food (this is chiefly due to climate, for there are few of the herbivorous animals which can compete with a rabbit); (3) destruction by carnivorous animals; (4) effects of climate, both direct and indirect; (5) parasitic diseases. It must be admitted that in New Zealand, where population is scanty, the climate mild and generally favourable, where there are large areas of natural grasses, no indigenous carnivorous animals to prey on the rabbits, and no indigenous parasitic diseases to thin their numbers, the rabbit escapes most of those adverse influences which keep it in check elsewhere. The population, however, is increasing rapidly, and carnivorous animals have to a certain extent been established, whilst several parasitic diseases have (though unintentionally) been introduced. The climate here is sufficiently moist to encourage the spread of some of these parasites. Wherever the population is even moderately thick the rabbit difficulty is not felt, for the action of man easily keeps the rabbits in check. There are, however, many districts in New Zealand which are not likely to attract a considerable population for very many years to come, but where there is a wholesome though not a rich pasturage for sheep, the land carrying perhaps a sheep to one, two, or even three acres. It is here particularly that the injurious effects of the rabbit-pest are felt, for, though the rabbits could of course be kept down by human agency, this result could only be attained at a cost which would more than swallow up the whole of the profit of sheep-farming on such land. It is here, then, that the destruction of rabbits by carnivorous animals or parasitic disease would be most welcome. The parasitic diseases of the rabbit which we have been discussing would have a limited but appreciable influence in this direction. It must not be expected, however, that they will prove the means of suddenly or completely exterminating all the rabbits in a district. Many infective diseases possess great powers of destruction, but there is no instance known of any infective or parasitic disease in nature which possesses the power of absolutely exterminating any species of animal. Any parasitic organism which should mercilessly cause the death of all the members of a species would thereby defeat its own object, for with the extinction of all suitable victims the

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