Unsuccessful expts. to determine the 1st intermediate host of M. latus are descr.; white mice and 36 spp. of 4 phyla of invertebrates were tested. The anatomy of adults, onchosphere, and tetrathyridium (from 2d intermediate host) stages is descr. The behavior and resistance of shed gravid segments from Didelphis virginianus is descr. Natural infestations of tetrathyridia in Peromyscus boylii in California and Leiolepisma laterale or Eumeces fasciatus in Texas are recorded.