ИСТИНА

Stolon is a special organ in hydroid colony, which has a set of particular functions. Despite of seeming morphological uniformity the microanatomy of stolons is suddenly diverse, as demonstrated by tissue studies using standard histological methods of both optical and electron microscopy. The aim of the study was to determine specific zones in the stolons differentiated by microanatomy and cell composition. Spatial tissue differentiation in G.loveni stolons takes place either in longitudinal (according to the distance from stolon apex) or in transverse (different segments of cross section) directions. Growing stolon has at least six morpho-functional zones: 1) apical part of the growing tip (GT) (length: L = 0.025 - 0,1 mm), consisting of an thickened epiderm only and demonstrating a high amount morular (perisarc-building) cell and nematoblasts (immature nematocytes); 2) subapical part of the GT with thickened gastroderm (L = 0.2-0.4 mm) presented by characteristic much-vacuolized cells; 3) proximal part of the GT (L = 0.1-0.3 mm) with wide gastrovascular cavity in which digested food is usually accumulated; 4) coenosarc between the GT and the first stalk with minimal body wall thickness; 5) first two stolonal internodes – intermediate zone between growing and mature stolonal coenosarc; 6) remote parts of stolon (beginning with fourth internode) – site of active cell proliferation and storage of nutrients. Transverse tissue differentiation is expressed in thickness of epiderm at different sides of stolon transverse section as well as different cell composition in epiderm of these sides. The results of this microanatomy study coupled with our earlier in vivo observations show distinct division of stolon to several compartments playing different roles in growth and morphogenesis of hydrozoan colony.