ALTHOUGH SPECIAL attention has been directed to flagellar structure and action in motile cells of Phycomycetes (Couch, 1941; Manton et al., 1951, 1952; and Koch, 1956), little work has been done on the internal structure of these cells. The purpose of the present paper is to help remedy this situation in the Chytridiales. A survey of the literature reveals that considerable variation has been found inchytrid zoospores, especially in their size and shape and in the size and number of their lipoid globules. As well, blepharoplasts, rhizoplasts, nuclei with nuclear caps, vacuoles and unidentified granules have been found in the zoospores of certain species, but so little attention has been directed toward the zoospore, even in cytological papers, that there is no clear picture of its structure for any species. The observations presented in this paper offer a somewhat new picture of body structure in the chytrid motile cell. Enough variability and complexity in structure and organization is shown to indicate that the internal structure of zoospores may serve as a basis for a critical comparison of chytrid taxa. MATERIALS AND METHODS.-The fungi studied and their sources are: Catenochytridium carolinianum Berdan, collected by M. B. Huneycutt on boiled paspalum leaf bait in soil from the University of North Carolina greenhouse. Chytridium sp., an undescribed species (Koch, 1957b)-, collected on paspalum leaf and sweet gum pollen bait in soil from North Carolina and Alabama. Entophlyctis sp., an undescribed species, morphologically somewhat like E. bulligera (Zopf) Fischer, collected on sweet gum pollen and boiled paspalum leaf bait in soil from North Carolina and Louisiana. Nowakowskiella ramosa E. J. Butler, collected on boiled naspalum leaf bait in soil sent from Texas by R. M. Tohns. Nowakowskiella sp., collected by E. K. Goldie-Smith on boiled paspalum leaf bait in soil from England. Phlyctochytrium punctatum Koch, collected on boiled paspalum leaf and sweet gum pollen bait in soil from North Carolina and Louisiana, and collected by G. B. Lucas and L. H. Person on the resting spores of Peronospora tabacina. Phlyctochytrium irregulare Koch, collected on sweet gum pollen and boiled paspalum leaf bait in soil from the Universitv of North Carolina greenhouse. Rhizophydium spiherotheca Zopf, collected on sweet gum pollen and boiled paspalum leaf bait in soil from North Carolina. Rozella allomycis Foust, collected on the sporophyte of Allomyces sp. growing on hemp seed bait in soil from North Carolina. Septochytrium variabile Berdan, of questionable