[Species of Oesophagostomum in sheep and goats in Stara Zagora District].

The study of small ruminant animals in the district of Stara Zagora has revealed that only one species of the Oesophagostomum genus could be found--Oesophagostomum venulosum (Rudolphi, 1809), Railliet et Henry, 1913. There are some morphological and metrical differences in the imaginal and larval stages between this species found in sheep and goats and the one described in the literature. It seems, therefore, that there exists great plasticity of these signs, and this should be taken into consideration in the identification of the species belonging to this genus.