ORGANIZATION AND ULTRASTRUCTURE OF THE REGENERATIVE CRYPTS IN THE MIDGUT OF THE ADULT WORKER HONEYBEE (L APIS-MELLIFERA)

The midgut epithelium of the adult honeybee consists of columnar and e ndocrine cells, both originating from regenerative crypt cells. The re generative crypt is composed of stem cells and differentiating cells. The stem cells generate two forms of endocrine cells along with differ entiating enterocytes of two distinct stages. At first they can be see n as Light crypt cells which are not secretory active; they then devel op into more electron dense, active secretory crypt cells. The develop ing enterocytes are arranged as tetrads, each composed of cells with t he same degree of differentiation. This can be explained by the occurr ence of cytoplasmic bridges between the cells of each tetrad. These fu somes are probably responsible for the apparent intercellular coordina tion. This is a new example of intercellular bridges between somatic c ells and, as far as we know the first description of fusomes in the in sect midgut epithelium. The microvilli on top of the crypt cells devel op within a spherical extracellular space where glycosaminoglycans are secreted. This occurs by the coordinated activity of the four surroun ding electron dense crypt cells. Microvilli formation therefore seems to be the first in a series of successive functions of honeybee entero cytes during their ontogeny.