Proliferative characteristics of the ependymal layer during the early development of the spinal cord in the mouse

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Morphogenesis of the collagenous stroma in the chick cornea

The embryonic chick corneal epithelium produces a highly structured acellular matrix beneath its basal surface during early development. This matrix, which contains collagen, serves as a morphogenetic template for subsequent stromal development in that the three-dimensional architecture of the adult corneal stroma is initially established, in miniature, in this epithelially derived connective tissue. Examination of the early corneal epithelium and matrix in both the light and electron microscope suggests that self assembly of the matrix may be one of several important factors in the morphogenesis of this early connective tissue.

Location and orientation of mitotic figures in the developing mouse olfactory epithelium

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Fine structural changes in the differentiating epidermis of Xenopus laevis embryos

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Germ-cell line and sexual differentiation in birds

The present paper deals with recent investigations on the germ line and the sexual organogenesis in birds. The analysis has been limited to the following problems: origin of the germ line, physiology of the germinal epithelia, determinism of the migration of gonocytes, and differentiation of the germ cells during sexual organogenesis. It has been clearly established that in birds the germ line is precociously determined and that the anterior germinal crescent is a secondary formation. The hypothesis according to which the primary localization of the germ cells in birds (and more generally in Amniotes) would be posterior, is discussed. It appears to be the most plausible. The germinal epithelia are secretory and excretory organs. The excretory function is of the merocrine type. Kinetic studies of the protein turnover in the germinal epithelia demonstrate the existence of at least two categories of cytoplasmic proteins: structural proteins, and exportable proteins; the latter are excreted via protrusions of the epithelial cells. The hypothesis according to which the excretory function is associated with the attractive power exerted by the sexual primordia upon the migrating primordial germ cells is examined. The mechanism controlling the entry into the genital ridge of the gonocytes circulating in the embryonic blood stream is of a chemotactic nature. Finally, during early sexual organogenesis, as well as during later stages of sexual differentiation, the germ cells undergo important ultrastructural, histochemical and physiological (migratory properties) changes.

Mucin biosynthesis by chick and human oesophagus during ontogenetic metaplasia

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Effects of cytochalasin B upon microfilaments involved in morphogenesis of salivary epithelium

Cytochalasin B causes cultured mouse salivary gland epithelium to lose its characteristic shape and to cease undergoing morphogenesis. The drug causes disorganization of the 50 A microfilaments in epithelial cells that are thought to control cell shape because of contractile properties. Upon removal of cytochalasin, epithelia regain normal shape and resume morphogenesis. Exceptionally large bundles of microfilaments appear in such recovered epithelial cells at points where their contractile activity could account for the changes in cell and tissue shape.

Ultrastructure of the epithelium of the human umbilical cord

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