Nuclei and tracts of the di-mesencephalon of the parakeet.

A number of nuclei and fibre systems of the parakeet di-mesencephalon, as visible in transverse series stained with the methods of HAGGQVIST and of KLUVER and BARRERA, have been described. In the preparations used, in which both neurones and myelinated fibres are visible, a relatively great number of elements can be distinguished, because of differences in cell and fibre content. Probably these elements are more sharply circumscribed than in the pigeon and therefore more readily visible. A few of them have been described for the first time, but they require experimental substantiation. Typical features of some nuclei and fibre systems of the parakeet have been pointed out. Attributing a certain type to the di-mesencephalon of the parakeet proved to be unfeasible, because of a deficient knowledge both about the elements studied and to their aspect in a sufficient number of other avian species. The pictures produced may be helpful in recognizing nuclei and fibre systems in other birds in which they are less distinct.