The, upon the whole, rare incidence of sexual reproduction in Desmids, and the possible explanation of this scarcity, are discussed. Records of zygotes of Cosmarium ochthodes Nordst var. amoebum West. C. pachydermum Lund. var. aethiopicum W. & G. S. West, Micrasterias papillifera Breb., and Tetmemorus laevis Kiitz. ex Ralfs are discussed in some detail. The duplicity of the wall of the zygospore of Tetmemorus laevis, as originally described by Ralfs (1848) but queried by Krieger(1937), is confirmed.