Earlier titles in this series have directed attention to selected questions of current theoretical or practical interest in developmental biology, without special emphasis upon individual biological systems. Tho choose giant polytene chromosomes as the common denominator of a new volume may at first sight seem to set rather arbitrary restrictions upon a coherent discussion of the basic problem of cellular differentiation. However, the reader will find out for hirnself that, on the contrary, such a limitation, though dicta ted by the material, focuses the analysis upon one essential point: the differential release of genetic information from operational subunits of the eukaryotic chromosome. In the organization of this volume we have not striven for completeness - some, indeed, may fee 1 that the work on Sciarids is underrepresented - but the various contributors have made every effort to render a thorough and up-to-date picture of the situation in their particular field, and on this basis to discuss all possible angles of general biological interest. Authors and editors have agreed to dedicate this volume to the memory of JACK SCHULTZ.

The majority of studies devoted to animal development traditionally start out from questions of morphogenesis. Of course, visible differentiation, as well as the events leading to it, should ultimately become describable in molecular terms. Nevertheless, even "simple" morphogenetic processes may have a complex biochemical basis which makes it difficult to recognize the key functions involved. This difficulty obviously does not exist in the case of glands, i. e. , organs and tissues primarily concerned with, and characterized by, the nature of their products, i. e. , one, or a few secretory proteins synthesized in huge quantities. In these systems, when we observe differences between different portions of a gland, or when switches of the synthetic activity occur during development, there is no question as to what we have to look for: we are directly faced with the fact of differential protein synthesis and the problem of its control. Insect glands, in addition, share other significant properties, i. e. , the absence of cell division during growth and, concomitantly, the formation of giant cells with polyploid or polytene nuclei. This unique set of peculiarities can be fully exploited only if one compares various representative systems, everyone of which, when considered by itself, might appear too exotic to invite generalization. In the present volume, the editors have endeavored to bring together contributionscoveringselected insect glands from various points of view,including the developmental, molecular genetic and cytogenetic aspects.

Die Entstehungsgeschichte dieses Bandes reicht weit zuriick. Schon wahrend der Arbeit an dem Cytoplasma-Teil des Handbuches in den friihen fiinfziger J ahren war unter Leitung von F. HfrCHNER ein Konzept fUr die Darstellung des Zellkernes entworfen worden, das zunachst auch ziigig ausgefiillt wurde. Indessen, mit dem Beginn der neuen, vor allem von Elektronenmikroskopie und Cytobiochemie getragenen Ara der Karyologie geriet die weitere E?-twicklung ins Stocken. Jeder Versuch, die Flut der neuen Erkenntnisse durch Anderungen oder Erganzungen des bereits Formulierten einzufangen, lief3 nur ein unerfreuliches und unhaltbares Flickwerk zuriick. Es blieb also keine andere Wahl, als auf alles bereits Fixierte zu verzichten. Einem neuen Beginn standen aber fiirs erste uniiberwindliche Schwierigkeiten entgegen: Die neuen Befunde iiberstiirzten sich und erschiitterten scheinbar festgefiigte Thesen, vermochten zunachst jedoch nur spezielle, aber keine allgemeingiiltigen Gesetzmaf3igkeiten zu vermitteln. Man muf3te also abwarten, bis eine gewisse Beruhigung der Situation eingetreten war, bis sich neue Ordnungs prinzipien abzeichneten, Verbindungsglieder zu friiheren, vielfach vergessenen Befunden sichtbar wurden und eine Zusammenschau alter und neuer Daten moglich erschien. Allerdings bedurfte es jetzt, im Ganzen und in Teilen, eines vollig F. BUCHNER, neuen Entwurfes, der wiederum dem ersten Betreuer dieses Bandes, zu danken ist, und dessen Realisation mit dem hier vorliegenden Abschnitt beginnt. Mit der detaillierten Darstellung der Chromosomen solI die Grundlage fiir das Verstandnis von Kernstruktur und Kernfunktion geliefert werden."