The growth and morphology of the excretory system of Stephanurus dentatus were investigated using both the light microscope and the electron microscope. In the 3rd-stage larva a branched tubular system extends from the posterior end of the excretory ampulla. The subventral glands are two elongated cells in the body cavity, and these do not appear to be attached to the tubular system.
The tubular and glandular portions of the excretory system are intimately associated with each other at the posterior end of the ampulla or sinus from the 4th-stage, but throughout their development they remain histologically distinctive. Moreover, the nuclei of each portion of the system are of two different types; those of the tubular system are similar to hypodermal nuclei, whereas the nuclei of the subventral glands are like the intestinal nuclei.
The lateral canals are extensions of the excretory sinus and lie embedded in the hypodermal tissue of the lateral chords. As the worm matures, the lateral canals increase in relative length, and the anterior branch of each lateral canal develops during the 4th stage.
Pink viscous fluid which passes from the excretory pore is identical in appearance with the fluid which is found in the lateral chords. It is suggested that the fluid in the lateral canals gains access to the excretory system by way of canaliculi in the wall of the lateral excretory canal.
I am most grateful to Professor J. F. A. Sprent for his interest and advice during this investigation, and to Mr J. J. Mines and Mr C. Boel for their able technical assistance. I gratefully acknowledge the financial support given for this study by the Australian Dairy Produce Board and the U.S. Department of Health, Education and Welfare (No. A 107023–02).