Differentiated aspect of female and male mouse mesonephroi.

In the mouse, Sryis expressed by somatic cells in the genital ridge and leads to initiate the transformation of the indifferent gonad into a testis. Here, we have examined the segmented female and male mesonephroi over the developmental period when the initiation of seminiferous cord formation takes place. We have generated three-dimensional models which reveal structural differences between male and female mesonephric tubules at 11.5, 13.5 and 14.5 days post coitum. We evaluate, following structural parameters, that form and orientation of the tubules could evolve differently in both sexes. We propose that the structural organization of the mesonephric tubules presents an early dimorphism.

Diversity in mimicry: paradox or paradigm?

Visual mimicry is a textbook case of natural selection because it is both intuitively understandable and has repeatedly evolved in a range of organisms: it is the ultimate example of parallel evolution. In many mimetic groups, particularly butterflies, a huge variety of colour patterns has arisen, even in closely related species. There has been much recent controversy over explanations of this variety. Mimicry is today a broad field of evolutionary study; here we discuss the evolution of its diversity in predator-prey systems.

A new three-dimensional treatment algorithm for complex surfaces: applications in surgery.

PURPOSE: Recent advances in computer technology enable automatic reconstruction of surface models using digitized contour lines and three-dimensional (3D) representation on a graphic terminal. This work was aimed at obtaining 3D reconstructions of facial bones to help guide oral surgery and complex dental implantology procedures. MATERIAL AND METHODS: The starting point was a computed tomographic examination. The limits of the cortical bone were automatically outlined and then digitized using a special computer program. The resulting data were then compiled for computer-aided design (CAD) purposes, and a virtual 3D model of the bone was mathematically computed. This model was next transferred to a computer program that piloted a CAD/computer-aided manufacture (CAM) machine that guided a laser stereolithography process. RESULTS: The early results of the use of 3D images, as well as solid models, for clinical and surgical purposes, indicate a high degree of reliability in morphologic diagnosis, determining the surgical procedure, and establishing the subsequent prognosis.

3D reconstruction of the mouse's mesonephros.

The present work reports on the three-dimensional reconstruction of the segmented mesonephros during the embryonic development of the mouse. With a light microscope and an automatic reconstruction of surfaces, aspects of the mesonephros are described. These surfaces are obtained by using digitized contour lines. A new interpolation method called DSI (Discrete Smooth Interpolation) enables correction of the distortion induced by microtomy in paraffin sections. After a triangulation step, this method uses a smoothing algorithm, which implies a spatial redistribution of the vertices of the triangles to correct the rotational and translational misalignment. The use of this 3D program improves the understanding of the development patterns and helps us to appreciate changes in the rebuilt mesonephros. By 10.5 embryonic days, tubules emerge from the Wolffian body and begin their formation, then between 11.5 and 13.5 embryonic days, tortuous mesonephric tubules bound to the Wolffian duct form small curls, which grow and finally unwind. At the same time, mesonephric tubules unbound to the Wolffian duct appear, and on 13.5 embryonic days, the Müllerian duct is visible. After 14.5 embryonic days, the segmented mesonephros keeps its general aspect but decreases in size. At this time, each gonad is provided with both Wolffian and Müllerian ducts. Later, the Wolffian duct differentiates into the definitive male duct system, whilst the Müllerian duct regresses. Conversely, the paramesonephric duct differentiates into the definitive female duct system, whilst the mesonephric duct in turn degenerates. By this time degeneration has begun in the cranial portion of the mesonephros and this process progresses caudally. The spatial organization of the mesonephric tubules and the precise organization of all connections between these elements and the ducts may be well defined. Such approach can allow for a high definition of the normal pattern of mesonephros differentiation.

A new display technique for computer-processed digital scans.

This article presents a new approach for presenting scintigraphic images. The technique combines the conventional plotting the contour lines and the highlighting, by means of hatching, of the concavities (or convexities) of the 'surface' representative of radioactive distribution. The search for the surface features is achieved generally by the method of normal curvatures. An example with a phantom demonstrates the utility of this representation method.

INCORPORATION OF A EUROPEAN WEED INTO THE DIET OF A NORTH AMERICAN HERBIVORE.

Populations of the butterfly Euphydryas editha living within a 30 times 100-km region on the eastern slope of the Sierra Nevada range were compared for oviposition preference and ability of larvae to grow and survive on two host plants, Collinsia parviflora and Plantago lanceolata. Since its introduction approximately 100 years ago, P. lanceolata has been incorporated in the diet of E. editha in one of the study populations. The populations differed in oviposition preference; only the population that uses P. lanceolata contains some individuals that prefer P. lanceolata. Larvae from two populations, one using both P. lanceolata and C. parviflora, the other using only C. parviflora, were not found to differ in relative abilities to grow or survive on P. lanceolata. The potential for E. editha to use P. lanceolata appears in populations that have had no prior exposure to this plant, while oviposition preference for this plant has evolved in the population in which the plant now grows.

[The chondrocranium of an 18 mm human embryo. A 3-dimensional computer-assisted reconstruction]. / Le chondrocrâne d'un embryon humain de 18 mm. Une reconstruction tridimensionnelle assistée par ordinateur.

INTRODUCTION: Three-dimensional reconstruction of histologic structures is still a real challenge. This is the reason why very few specimens are published, especially for the head. MATERIAL AND METHODS: The chondrocranium of an 18-mm human embryo was reconstructed from serial histologic sections. The three-dimensional reconstruction was based on a software used in geology and adapted to medical applications. This software was able to smooth the reconstructed model, i.e. to correct the distortions due to the histologic preparation. RESULTS: The chondrocranium model is presented. To facilitate spatial orientation, we added the reconstruction of Merkel cartilage, of Reichert cartilage, of the vertebrae, and of the cerebrum. The different portions of the chondrocranium are described. DISCUSSION: The three-dimensional result is described and advantageously compared to the rare wax models available. The morphological differences are detailed. CONCLUSION: This technique of three-dimensional reconstruction with its smoothing procedure is a very well adapted method for reconstruction of histologic structures. The results presented confirm the educational value of this tool, which is otherwise a powerful instrument of morphogenic study.