Abstract
1. Three groups of Wistar rats were subjected to a single dose intraperitoneal injection of 0.2 mg/kg, 0.225 mg/kg and 0.25 mg/kg of vincristine on day 8 of pregnancy, respectively. Follow-up studies from day 11 to 20 were conducted. 2. In those examined on day 13, there were cases with slight elevation, protrusion or unevenness on the top of the cranial surface and there were also cases with cloud or plications in the brain wall observable from the outside. After day 14 or 15, cases were detected that fall into the category of brain hernia,transitional conditions of a kind of cranioschisis with a small opening. 3. Such abnormal changes initiated from grouping and migration of neural cells had the appearance of neural elements usually situated in the deeper part of the neural tissue. These changes seem finally to lead to outgrowth or plications of the neural tissue, and such changes were tentatively called disorganization of the neural tissue or midbrain. In the above changes, rosettes were often evident. 4. Based on this observation, it is presumable that besides the common process of anencephalia formation in the sense of Giroud's concept, i. e. , caused by failure of the neural tube closure (primary in nature), there exists that of a secondary nature, resulting from reopening of the neural tube once closed. The eversion of the brain tissue, however, was not extensive. 5. Coexistence of rosettes in the initial change taking place in the above process called disorganization of the neural tissue suggested that such process might be due to proliferative nature.
