Larvae similar to those found in infective eggs of members of the order Oxyurida were found apparently free in the uterus of a female oxyuridan (perhaps belonging to the genus Alaeuris) recovered from Amphisbaena alba from Venezuela. The worm may reproduce by autoinfection as do several other Oxyurida (Gyrinicola spp., Tachygonetria vivipara, and certain Alaeuris spp.) of amphibians and lizards. The vast majority of zooparasitic nematodes are serial colonizers; parasitic females produce eggs or larvae that must pass to the external environment to complete the life cycle. Autoinfection, the ability to cycle within the host, occurs, however, in certain Oxyurida of the Pharyngodonidae. Typically, members of the order Oxyurida are transmitted by thick-shelled eggs contaminating the host's environment. However, a few species from amphibians and lizards are known to produce 2 types of eggs: a thick-shelled variety that must pass to the external environment to complete the life cycle and a thin-shelled variety that hatches at or soon after deposition and gives rise to an endogenous cycle (autoinfection). Recently, I obtained, on loan, nematode specimens from Amphisbaena alba (Amphisbaenidae) deposited in the Museum d'Histoire Naturelle in Paris (Laboratoire des Vers: 800F). In addition to a dozen Atractid specimens was a female nematode (Figs. 1-8) attributable to the family Pharyngodonidae, perhaps belonging to the genus Alaeuris. A remarkable feature of this worm is that larvae developing in utero are not surrounded by an egg shell but apparently lie free in the uterus. The only other Oxyurida in which an egg shell is lacking (or extremely reduced) are those that exhibit autoinfective cycles and the present material therefore seems to represent another such species. The specimen, 3.02 mm long, is described as follows. Maximum width 322 uim near midbody. Buccal cavity 6.3 ,m, oesophageal corpus 748 Am, and isthmus 100 tm long. Bulb 103 3um long and 113 m wide. Nerve ring 187 Am, excretory pore 865 ,m, and vulva 1.5 mm from anterior extremity. Vagina consisting ofthick-walled portion nearest vulva 177 Am long, and posteriorly directed vagina uterina 645 Am long. Tail conical, 481 Am long. Pharyngodonid genera are difficult to distinguish uniquely on the basis of female morphology. Nevertheless the present material is likely a member of Alaeuris or Paralaeuris because these are the only pharyngodonid genera from New World lizards (with the exception of Ozolaimus, distinguishable on the basis of oesophageal and cephalic morphology) in which the female has a conical tail. I have not given the specimen a species name because only a single female specimen was available for study. Autoinfection is known in only 3 oxyuridan g nera. Species of the genus Gyrinicola parasitize anuran larvae throughout the world and all have an autoinfective phase in their life cycle (Adamson, 198 la, 198 lb). Such a phase also occurs in Tachygonetria vivipara, a parasite of Uromastix acanthinurus in North Africa, and in 2 species of Alaeuris, namely A. vogelsangi and A. caudatus parasitizing Iguana iguana in South America (Seurat, 1913; Petter, 1969; Adamson and Petter, 1983). Unlike the situation in Atractidae (Cosmocercoidea; Ascaridida) where autoinfection occurs in each generation, autoinfective generations apparently alternate with dispersing generations in the above Oxyurida. This is accomplished in at least 2 ways. In Gyrinicola, females produce 2 types of eggs (a thin-shelled autoinfective type and a thick-shelled dispersing type) in separate horns of the reproductive tract. One egg type tends to predominate in a given female and there is an alternation of generations such that females that develop from thin-shelled eggs produce almost exclusively thick-shelled eggs, whereas those that develop from thick-shelled eggs produce predominantly thin-shelled eggs (Adamson, 1981 c). In Alaeuris, Tachygonetria, and presumably the material described here, there are 2 types This content downloaded from 157.55.39.203 on Thu, 20 Oct 2016 04:00:47 UTC All use subject to http://about.jstor.org/terms