Historical Review.- Material and Methods.- Results.- A. The Infundibular CSF Contacting Neurons of Fishes.- I. The CSF Contacting Neurons of the Periventricular Hypothalamic Nucleus.- Light Microscopy.- Electron Microscopy.- Discussion.- II. The CSF Contacting Neurons of the Nucleus Lateralis Tuberis.- Light Microscopy.- Ultrastructure.- Discussion.- III. The CSF Contacting Neurons of the Vascular Sac.- Light Microscopy.- Electron Microscopy.- Discussion.- B. The CSF Contacting Neurons of the Infundibular Lobe of Amphibians.- Light Microscopy.- Electron Microscopy.- Discussion.- C. The CSF Contacting Neurons of the Infundibular Nucleus of Amniote Vertebrates.- 1. Comparative Light Microscopy.- Histology.- AChE reaction.- 2. Comparative Ultrastructure.- Reptiles.- Birds.- Mammals.- 3. Discussion.- General Conclusions.- Summary.- References.