Gerhard Schlosser

Most of the cranial sense organs of vertebrates arise from embryonic structures known as cranial placodes. Such placodes also give rise to sensory neurons that transmit information to the brain as well as to many neurosecretory cells. This book focuses on the development of sensory and neurosecretory cell types from cranial placodes by introducing the vertebrate head with its sense organs and neurosecretory organs and providing an overview of the various cranial placodes and their derivatives, including evidence of common embryonic primordia. Schlosser discusses how these primordia are established in the early embryo and how individual placodes develop. The latter chapters explain how various placodally derived sensory and neurosecretory cell types differentiate into discrete structures.

Most of the cranial sense organs of vertebrates arise from embryonic structures known as cranial placodes. Such placodes also give rise to sensory neurons that transmit information to the brain as well as to many neurosecretory cells. This book focuses on the development of sensory and neurosecretory cell types from cranial placodes by introducing the vertebrate head with its sense organs and neurosecretory organs and providing an overview of the various cranial placodes and their derivatives, including evidence of common embryonic primordia. Schlosser discusses how these primordia are established in the early embryo and how individual placodes develop. The latter chapters explain how various placodally derived sensory and neurosecretory cell types differentiate into discrete structures.

Most vertebrate cranial sense organs arise from placodes. These placodes give rise to sensory neurons that transmit information to the brain and neurosecretory cells. This book reviews the evolutionary origin of the sensory and neurosecretory cell types. It summarizes our current understanding of vertebrate evolution, clarifies conceptual issues relating to homology and evolutionary innovation of cell types, compares the sensory and neurosecretory cell types with similar cell types in other animals, and addresses the question of how cranial placodes evolved as novel structures in vertebrates by redeploying pre-existing and sometimes evolutionarily ancient cell types.

Most of the cranial sense organs of vertebrates arise from embryonic structures known as cranial placodes. Such placodes also give rise to sensory neurons that transmit information to the brain as well as to many neurosecretory cells. This book focuses on the development of sensory and neurosecretory cell types from cranial placodes by introducing the vertebrate head with its sense organs and neurosecretory organs and providing an overview of the various cranial placodes and their derivatives, including evidence of common embryonic primordia. Schlosser discusses how these primordia are established in the early embryo and how individual placodes develop. The latter chapters explain how various placodally derived sensory and neurosecretory cell types differentiate into discrete structures.

Most vertebrate cranial sense organs arise from placodes. These placodes give rise to sensory neurons that transmit information to the brain and neurosecretory cells. This book reviews the evolutionary origin of the sensory and neurosecretory cell types. It summarizes our current understanding of vertebrate evolution, clarifies conceptual issues relating to homology and evolutionary innovation of cell types, compares the sensory and neurosecretory cell types with similar cell types in other animals, and addresses the question of how cranial placodes evolved as novel structures in vertebrates by redeploying pre-existing and sometimes evolutionarily ancient cell types.

Most of the cranial sense organs of vertebrates arise from embryonic structures known as cranial placodes. Such placodes also give rise to sensory neurons that transmit information to the brain as well as to many neurosecretory cells. This book focuses on the development of sensory and neurosecretory cell types from cranial placodes by introducing the vertebrate head with its sense organs and neurosecretory organs and providing an overview of the various cranial placodes and their derivatives, including evidence of common embryonic primordia. Schlosser discusses how these primordia are established in the early embryo and how individual placodes develop. The latter chapters explain how various placodally derived sensory and neurosecretory cell types differentiate into discrete structures.

Eine tiefe Unzufriedenheit bereitete den fruchtbaren Boden, in dem die Überle­ gungen des vorliegenden Buches wurzeln und gedeihen konnten. Eine Unzufrieden­ heit, die ich seit Jahren immer dann empfinde, wenn in den Wissenschaften von "Reduktion" die Rede ist, wenn etwa behauptet wird, die Biologie sei auf die Physik oder Geisteswissenschaften seien auf Naturwissenschaften zu reduzieren. Je mehr ich mich mit diesem Thema beschäftigte, desto größer wurde mein Unbehagen gegenüber reduktionistischen Thesen. Zweifelsohne gibt es eine Einheit der Welt, es sollte daher "irgendwie" auch eine Einheit der Wissenschaft geben. Eine solche Position könnte man -schreckt man vor "ismen" nicht zurück -ganz allgemein als "Unifikationismus" bezeichnen. Der Weg jedoch, den viele "Reduktionisten" einschlugen, um zur Einheit zu gelangen, schien mir auf großen Strecken nicht gangbar, schien von allzuvielen materialistischen Vorurteilen und Widersprüchlichkeiten verstellt zu sein. Einige die­ ser Vorurteile aus dem Weg zu räumen, einige dieser Widersprüchlichkeiten aufzu­ zeigen und zu beseitigen ist das Ziel dieses Buches. Systemtheoretische Überlegungen gelangen derzeit in den verschiedensten Wissen­ schaften zu fruchtbarer Anwendung (vgl. etwa Haken (1976, 1981, 1985), Schmidt (1987» und könnten daher zum Ausgangspunkt für ein interdisziplinäres Gespräch werden, ohne die Existenzberechtigung verschiedener Disziplinen nach reduktionisti­ scher Manier in Frage stellen zu müssen. Die neuere systemtheoretische Diskussion krankt aber daran, daß sie keinen präzisen und konsistenten Systembegriff anzubieten hat, der interdisziplinär anwendbar wäre und sich somit eignete, Brücken zwischen den Disziplinen zu schlagen. Diesem Mangel möchte ich mit dem vorliegendenBuch abhelfen.