MESOGLEA OF HYDRA .2. POSSIBLE ROLE IN MORPHOGENESIS

Examination of histological sections and isolated mesogleas in Hydra pseudoligactis reveals that the mesoglea is not a uniform structure but changes in form in different body regions and during asexual reproduction. At the extremities of the body column, the rim of the mouth and aboral pore, the fiber system of the mesoglea is strongly developed and appears to occlude the cementing matrix which usually surrounds the fibers. Cells, on reaching these extremities, pass over the fiber mass and slough off the body column. The mesoglea of the gastric region is well‐developed but the fibers here are thinner than those in the peduncle. During budding the fiber system breaks down throughout the gastric and budding region while the fiber system in the peduncle persists. It is suggested that cells moving down the gastric column, because their basal processs can no longer attach to the fiber system, cannot readily enter the peduncle where attachment sites are already occupied. These cells will pass out into the budding tissue. It is suggested that the spindle orientation of dividing cells is probably perpendicular to the oral‐aboral axis of the parents in the area of the bud. The adhesiveness of the two cell layers in various body regions is discussed. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company