Adenine was injected intraperitoneally to pregnant ICR-JCL mice on day 10 of gestation at a dosage of 200 or 250 mg/kg. The fetuses were examined externally on day 19 of gestation. Embryonic death, growth suppression and malformations such as encephalocele on forehead, cleft palate, cleft lip, limb defects and tail defects were induced. It is noteworthy that left-sided malformations were found in nine out of 11 fetuses with forelimb defects.

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In an electron microscope study of the gill tissue of shellfish Hormomya mutabilis Gould obtained from Minamata Bay, Kumamoto Prefecture, parallel-arranged crystalline and homogeneously dense inclusions were found in mitochondria appearing in the epithelial cells. The ultrastructure of such inclusions and possible functions were discussed.

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(1) With Sudan black B stain lipid was a bluish tint in the deparaffinized sections, and was caesious in color in the non-deparaffinized sections. The cells and tissues, where lipid was localized, were approximately the same in both sections, and their distribution corresponded with the distribution in the frozen sections.
In the bud stage lipid was present in the buldged part of the dental epithelium, and in the cap stage it was recognized in the inner and the outer enamel epithelium, in the boundaries between the inner and the outer enamel epithelium, and in the enamel knot. Lipid was hardly recognized in the stellate reticulum and in the dental papilla.
(2) In the deparaffinized sections, the transparent droplet-like or little crystalline substances (2-3μ ) were situated, slightly in the inner part, and remarkably in the buidge and in the free end of the dental epithelium in the bud stage. In the cap stage they were recognized in the dentale Pithelium, especially in the enamel knot. They were slightly recognized in the oral epithelium, but they were not in the dental papilla and in the surrounding tissues of the tooth germ. In the non-deparaffinized sections; The droplet-like or little crystalline substances (2-3μ ) were remarkably recognized in the oral epithelium. They were scattered in the dental epithelium, unlike the deparaffinized sections, they were not abundant in the swollen part and in the free end of the bud stage, and they were not remarkable in the enamel knot of the cap stage. In the surrounding tissues of the tooth germ, including dental sac, they were situated as a group at a certain dis- tance from the margin of the tooth germ on the buccal side, or were observed along the dental sac, describing a circular arc.
They were not recognized in the frozen sections. It seems that they are neutral fat or cholesterin crystal.
(3) In the non-deparaffinized sections, the streak-like or the embossed carving figures were seen in the dental epithelium, especially they were often recognized in the free end and in the buldge of the bud stage, and in the inner enamel epithelium and in the circumferences of the enamel knot of the cap stage. It is assumed that they indicate the position of the invagination in the dental epithelium.
(4) Some specific spindle cells in the dental epithelium and some irregular-shaped mesenchymal cells in the dental papilla contiguous to the dental epithelium were stained more bluish or Nile green in color than any other cells in the tooth germ, and some of them were not stained except the nucleolus. They were often recognized in the periphery of the streak-like or the embossed carving figures in the dental epithelium of the non-deparaffinized sections.
(5) It is thought in the paraffin sections that post-chroming stain with Kernecht-Rot is difficult.

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The brain of Xenentodon is divided into the telencephalon (olfactory lobes and cerebrum), diencephalon, mesencephalon and rhombencephalon (cerebellum and medulla oblongata). Olfactory lobes are small and the olfactory peduncles are absent. Cerebrum is divided into axial, parietal and occipital lobes by rhinal, occipital and frontal fissures. There is a single median and narrow ventricle in the cerebrum. Diencephalon is demarcated by a velum transversum in front and by the posterior commissure behind. Out of four regions of the diencerhalon (epithalamus, ventral thalamus, dorsal thalamus and hypothalamus), dorsal thalamus is poorly developed. Haebenular ganglia form two large ovoid masses in the epithalamus. The hypothalamus is very well developed, with an infundibulum and the lobi inferiores. There is no saccus vasculosus. On the roof of diencephalon there is some indication of the paraphysis but parapineal is absent. The pineal is an elongated structure with a definite stalk. Numerous pigment granules are found in the pineal cells. Tectum opticum is divided into two lobes. Torus semicircularis and tori longitudinales are well developed. The cerebellum is roughly triangular in shape. Its anterolateral corners form the acoustic-tubercles. The cerebellum throws out an anterior extension, the valvula cerebelli, into the cavity of mesencephalon. The valvula cerebelli are biforcated anteriorly. Posterior choroid plexus is more developed than the anterior choroid plexus.

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1. The mamillothalamic tract arises from all of the mamillary nuclei. The pars medialis of the medial mamillary nucleus sends fibers ipsilaterally to the pars magnocellularis of the anteroventral nucleus and the anteromedial nucleus of the thalamus. Its medial portion projects to the medial portion of the pars magnocellularis of the anteroventral nucleus and the dorsomedial part of the anteromedial nucleus, while the lateral portion projects to the dorsolateral portion of the pars magnocellularis of the anteroventral nucleus. The pars lateralis of the medial mamillary nucleus sends fibers to the pars parvocellularis of the anteroventral nucleus of the same side and also to the anterodorsal nucleus of both sides. The lateral mamillary nucleus is connected with both anterodorsal nuclei.
2. The mamillary nuclei contribute fibers to the medial forebrain bundle, projecting to the medial septal nucleus. Some of these mamilloseptal fibers end in the lateral hypothalamic and the lateral preoptic nuclei on their way to the septal nucleus.
3. The mamilldtegmental tract divides into the main dorsal and the ventral bundles. Although the latter is directed ventrally to the nucleus reticularis tegmenti pontis and the pontine nuclei, the former passes dorsally to the dorsal and ventral tegmental nuclei, and the central gray of the pons. The fibers from the pars medialis of the medial mamillary nucleus end chiefly in the ventral tegmental nucleus, particularly the small-celled part, but some of them run further dorsally to enter the large-celled ventral part of the dorsal tegmental nucleus. It should be mentioned that a few fibers from the pars medialis of the medial mamillary nucleus partly run dorsally along the median raphe to enter the central gray of the pons, and partly cross the midline to end in the ventral tegmental nucleus of the opposite side, though a very few fibers pass through this nucleus. The fibers from the pars lateralis of the medial mamillary nucleus are directed largely to the dorsal tegmental nucleus, particularly its large-celled ventral part, and partly to the ventral tegmental nucleus. Within the dorsal nucleus most fibers terminate, but some pass through it to end in the central gray of the pons. On the other hand, a few fibers from the pars lateralis of the medial mamillary nucleus run dorsally along the median raphe to terminate in the central gray of the pons, without entering the tegmental nuclei. The fibers from the lateral mamillary nucleus are distributed to the ventral and dorsal tegmental nuclei, and to the central gray of the pans along the median raphe. Besides, they are distributed to the reticular formation and the tegmental laterodorsal nucleus.
4. A small number of fibers from the mamillary nuclei descend in the mamillary peduncle and can be traced to the middle levels of the interpeduncular nucleus. During their course many of them spread dorsally to join the mamillotegmental fibers.
5. The mamillary body contributes fibers to the dorsal longitudinal fasciculus of Schütz. These fibers descend in the mesencephalie central gray of the same side as far caudally as the lowest level of the superior colliculus, spreading out laterally into the reticular formation throughout their course.

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The change in extent and pattern of new bone formation with age was studied by quantitative and qualitative observation of osteoid covering vertebral irabecular surfaces. The various types of trabecular structures, such as transverse and longitudinal trabeculae,. were separately studied by a technique of staining thin slabs of vertebrae. The percentage of osteoid is highest in infancy and then decreases to a minimal value in early adulthood. It remains at this basal level through age 40. During the 5th through 7th decade, formation increases three-fold above the basal level as progressive loss of bone mass occurs. In infancy and childhood, osteoid seams are evenly distributed throughout the vertebra, regardless of the type or location of the trabecular structures. However, in young adults, osteoid is small in amount and is seen only at the surfaces of the transverse trabeculae. In the 5th and 6th decades, osteoid is chiefly on the transverse trabeculae, indicating the high turnover of these structures which are being lost first in the involutional process. With decreasing mass of bone in aging, persisting longitudinal trabeculae are converted into plates by apposition of new bone, which is reflected by the presence of osteoid surfaces on longitudinal trabeculae in old age.

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