MORPHOGENESIS OF HELICAL FIBERS IN HAPLOTAXIDS

There are two different muscle fiber types in haplotaxis. The pseudo-c ircomyarian type is typical of Haplotaxis gordioides and the flattened circomyarian type of Pelodrilus leruthi. The mechanisms of growth in fiber size and in fiber number of the two fiber types in the hindmost region of adult specimens have been studied ultrastructurally. The inc rease in length and girth of the muscle fiber is always the result of the insertion of new myofilaments in the peripheral zones of the muscl e cells. The increase in the number of fibers seems to be due to divis ion of differentiated muscle cells.