1. The postnatal changes of X-ray induced microcephaly were observed in sequence in CF # l mice which had been exposed to a single dose of 200R of X-ray from day 12 to 17 of gestation. 2. In the groups irradiated on day 12 and after day 14 of gestation, X-ray induced microcephaly remained unchanged or became less predominant as the animals grew older. In the group treated on day 13, the lateral ventricles of microcephalic brains started to enlarge one to two weeks after birth, and hydrocephalus became intensive progressively with the advance of age. Postnatal hydrocephalus was manifested in brains involved with marked aberration of cortical structure. 3. Prior to manifestation of hydrocephalus, venous congestion, hemorrhages and consequent tissue degeneration were evident in the subependymal white matter of neopallium. Neither stenosis nor obstruction in the ventricular system could be detected. 4. The results suggested possible causal relationships among maldevelopment of the cortical structure, circulatory disorders in the brain mantle and manifestation of hydrocephalus.

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1. Wistar rats were treated with an intraperitoneal injection of 40 mg/kg trypan blue solution on day 8 of pregnancy. 2. Seventeen treated female rats were put to death on day 20 of pregnancy and fetuses removed surgically from mothers. After gross observations, the fetuses were examined in bone specimens or in microscopic sections. 3. In 152 living fetuses, 63 showed myeloschisis or hypoplasia of the lower trunk accompanied by taillessness or short tail. The bone specimens of these malformed fetuses showed fusion, deformity or absence of lumbar and sacro-coccygial vertebrae. In microscopic observation, the spinal cords of these malformed fetuses showed myelodysplasia in the lumbo-sacral region. 4. Seventy-seven treated female rats were allowed to give birth. Malformed offspring were observed daily and autopsied at various intervals between 23 and 125 days after birth. The skeletons were examined in X-ray photographs or in cleared bone specimens. After gross observations, the spinal cord was examined microscopically. 5. Twenty-five of 77 treated mothers reared abnormal offspring for more than 3 weeks after birth. Twenty-six of 33 malformed offspring revealed symptoms of myelodysplasia. Neurological symptoms such as paralysis of hindlimbs or incontinence of urine and feces became evident gradually for one or two weeks after birth. X-ray photographs or bone specimens of offspring with myelodysplasia showed fusion, absence or deformity of lumbar vertebral bodies and complete or partial absence of sacro-coccygis. In such cases, the spinal cord and the terminal filum were much shorter than in normal ones. Microscopically, a delay of myelination in the posterior and lateral funiculus were found in some cases.

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Two autopsy cases of D_1-trisomy syndrome were reported. In the family history short stature of the mother was characteristic. The pathological characteristics in both cases were arhinencephalia, polydactylia, facial cleft, cardiovascular anomalies, dysplastic cerebellum, umbilical hernia, Meckel's diverticulum, common mesentery, poor ossification of cranial bones, and tendency of cyst formation in the thyroid and kidney. Several significant findings were observed in the two cases under study, but these varying features could not be evaluated at present.

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1. In order to examine the teratogenicity of amniocentesis and the morphogenesis of resultant limb malformations, rat fetuses were subjected to a single amniocentesis during day 13 and 16 of gestation. 2. Gross malformations manifested were cleft palate and reductive malformations of extremities which are compatible to intrauterine amputations in human. They were predominant in degree and frequency in the group treated on day 15 of gestation, regard-less of the amount of amniotic fluid removed. 3. In the histological examination of the limbs, hemorrhages from the marginal blood sinus which were manifested 15 minutes after treatment caused necrosis of the mesenchymal tissue, and consequently intrauterine amputations or constriction rings resulted according to the extent of hemorrhages. Neither constriction by amniotic band and fibrous strings nor attachment of amnion to the limbs could be found in the process of limb malformations. 4. Experiments suggest that contraction of uterine muscle may well play an important role in the manifestation of hemorrhages from the marginal blood sinus.

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