This volume marks the end of twenty years of neurosecretion during which there were five symposia, namely Naples (1953), Lund (1957), Bristol (1961), Strasbourg (1966), and Kiel (1970). In comparison with these symposia an exceptionally large number of papers were read at this the sixth symposium, in London, and for economic reasons it has not been possible to publish all the papers in extenso. The editors have therefore been obliged to undertake the unenviable work of selection, a task made all the more difficult by the excel lence and importance of contributions of the symposium. We felt that it was of the utmost importance at this moment in the history of neurosecretion to present as complete a picture as possible of the present state of the subject in relation to the past and opportunities for the future. We have therefore given some preference to papers with a strong review element, research papers in areas of current importance and contributions which deal with recently developed techniques with promise for the future. We have more over attempted to strike some balance between the different areas of research on neurosecretion so that the volume as a whole may be of interest to the general reader, and that he will find in it a reasonably coherent pattern of thought which demonstrates neurosecretion as the final neuroendocrine pathway. We have attempted a certain degree of uniformity of spelling, symbols, etc."

When I was asked by the late Professor Wolfgang Bargmann in 1973 to write the continuation of his review article on the epiphysis cerebri published in the present Handbuch Series in 1943 I felt greatly flattered and readily agreed, not knowing that it is virtually impossible for a single person to cover comprehensively the vast field of pineal research carried out over the last 35 years. Although I have done my best to include as much of the relevant work as possible (up to July 1979), I am constantly haunted by the references I have missed. I sincerely apologize for these omissions: first, to the authors of these papers, who, in addition to working on one of the most stony grounds of biological research, now may experience the additional frustration of not being quoted; secondly, to my fellow pinealogists or pinealogists-to-be, who may carry out painstaking experiments only to find that they have been done before, or who may be led astray because of lack of information. Nevertheless, I do hope that this monograph will fulfil its aim, namely to show how pineal research has progressed over the last 35 years and where it stands today. It is hoped that it will aid in planning relevant experiments and that it shows which approaches to the pineal problem would be better avoided.

Durch die Anwendung biochemischer und histochemischer Methoden sowie der Elektronenmikroskopie hat die entwicklungsgeschichtliche Forschung in den letzten Jahren eine starke Entfaltung erfahren. Dies verwundert nicht, da ein tieferes V er- standnis der entwicklungsgeschichtlichen Vorgange nur bei Berucksichtigung der auch im molekularen und submikroskopischen Bereich ablaufenden Differenzie- rungsprozesse zu gewinnen ist. Der Schwerpunkt der chemisch ausgerichteten embryologischen Studien liegt in der Fruhentwicklung. Vergleichsweise wenige Arbeiten befassen sich mit der genannten Problematik in der letzten Phase der Entwicklung, in der die Organogenese vor ihrem Abschluss steht und durch die Funktionsaufnahme ihr besonderes Geprage erhalt. Da in dieser Periode mit kon- ventionellen histologischen Methoden meist keine Veranderungen mehr zu be- obachten sind, sind histochemische und elektronenmikroskopische Untersuchungen besonders geeignet, evtl. vorhandene weitere Differenzierungsvorgange aufzu- decken und den Entwicklungsablauf auch in funktioneller Hinsicht besser zu charakterisieren. Die vorliegende Studie uber die Entwicklung des Dunndarms der Ratte soll hierzu einen Beitrag leisten. Im Mittelpunkt dieser Untersuchung stehen die Entwicklung der Feinstruktur und die Chemodifferenzierung des fetalen und postnatalen Jejunums. Auf die Histo- genese des Organs wird nur am Rande eingegangen, da entsprechende Unter- suchungen vorliegen (HILTON, 1902; HuMMEL, 1935; KAMMERAAD, 1942). Im Rahmen feinstruktureHer Untersuchungen, die bisher nur fur die Entwicklung der Saum- (BEHNKE, 1963; DuNN, 1967; HAYWARD, 1967 a, b) und Panethschen Koer- nerzellen (BEHNKE u. MoE, 1964) durchgefuhrt wurden, interessiert in funktioneller Hinsicht vor allem die Differenzierung der fur die Resorption wichtigen Strukturen wie Zotten und Saumzellen mit ihren Organellen.