Eight of twenty armadillos ( Dasypus novemcinctus L.) developed severe lepromatous leprosy 3 to 3.5 years after inoculation with viable Mycobacterium leprae . A total of 988 grams of lepromas containing an estimated 15 to 20 grams of leprosy bacilli has been harvested from these animals. The large amounts of material now available will permit in-depth studies of the biochemistry and metabolism of the leprosy bacillus, and the animal model should make possible definitive studies on the immunology, chemotherapy, and epidemiology of the disease.

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In 1951, studies in our laboratories revealed, for example, that among Wistar rats that had been brother-sister mated for 101 generations and were consuming exactly the same diet, individual urinary excretion patterns showed wide diversity. As an instance, in a small group of these animals, urinary phosphate excretion varied 11-fold and lysine excretion at least 14-fold.'Other investigations have shown that within groups of closely inbred animals (including fowl), enormous variations-up to 60-fold or more-may readily be observed with respect to such items as the voluntary consumption of alcohol, choices of various types of foodstuffs, and tendency to exercise.2 We have recently been concerned also with the wide differences in the nutritional needs of individual inbred animals for vitamins A and C.3, 4 All these wide disparities call for more adequate explanation.We have wondered whether unknown factors aside from the gene pool itself do not control the intricate process of differentiation, particularly the extent to which each of the numerous types of differentiated cells proliferates. If there is this sort of control, even animals with identical complements of genes could have organs that differ in size, and every hormone could be produced in characteristic amounts in each individual animal, depending upon the extent to which the various hormoneproducing cells had proliferated during development. Hormone patterns are of particular interest because we have some reason to think that hormonal differences are related to several of the areas in which we observe wide differences (food choices, etc.).Clearly it would be difficult to test this interpretation as long as inbred animals with only similar gene pools are studied, because disparities which are observed might always be attributed to slight differences in the gene complements.In order to find a more clear-cut answer to the question, we have studied a number of structural and biochemical parameters in newborn quadruplet armadillos. The reproduction of the nine-banded armadillo has been thoroughly studied by Newman and Patterson,'-7 who found the normal mode to involve the regular production of monozygous quadruplets. Sets of animals are thus produced which should have, barring rare mutations, exactly the same genes. It is interesting that in early work, Newman and Patterson commented on variations in scute numbers and aberrations in banding. These differences, though small, may be highly significant.In the process of producing monozygous quadruplets, the single fertilized ovum develops to the blastocyst stage, later becomes implanted, and four primordial buds are formed in two stages. These develop independently. While the chromosomal material of the zygote is duplicated in these buds, it seems un-910

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Summary. Armadillos are generally believed to have a gestation period of 8-9 months that includes a 3-to 4-month period of embryonic diapause. Nevertheless, 21 fe males bore litters 13-24 months after capture and subsequent isolation from males. Two of these animals were pregnant in successive years. Evidence is presented that this is a facultative survival mechanism, induced by stress, that has not been previously reported among mammals.Armadillos (Dasypus novemcinctus) are placental mammals (Order Xenarthra) that are usually monestrous and monovular. I In North America, parous fe males ovulate during July and August and nulliparous animals in November. After summer ovulation and mating, embryos develop to the blastocyst stage and then enter a diapause period of 3-4 months. Implantation of a single blastocyst usually takes place in late November or early December, I after which the cell mass buds twice to yield 4 embryos.2.3 Monozygous quadruplets are born in the spring about 5 months after implantation. I Thus gestation is believed to last for 8-9 months including embryonic diapause.However, we have found that some females bear young 1-2 years after the generally accepted time fo r parturition, a phenomenon not previously reported among mammals. Materials and methodsThis finding resulted from the use of wild-caught armadillos in leprosy research4 so that large numbers of them are housed in laboratories throughout the world. To minimize injuries, all animals in our colonies in Florida and England were housed separately in plastic cages fo r 1-3 years before they were killed for harvest of leprosy bacilli. Cage design and the protocols used precluded copulation after capture. These procedures are described in detail elsewhere.s Animals were collected in groups of 10-40 in Central Florida from 1979 to June 1986. The dates of capture were governed by the requirements of the leprosy programme; therefore, sampling of the wild population was not uniform from month to month.