Cytological Polymorphism in the Nematode Haemonchus contortus (Rudolphi 1803) Cobb 1898

Abstract

RECENT observations by Roberts, Turner and McKevett¹ have indicated that the so-called ovine and bovine ‘strains’ of Haemonchus contortus (Rud. 1803) are distinct species. This conclusion is based mainly on differences in the morphology of the infective larvæ and in the type of cuticular vulval process dominant in adult females in natural populations in each host. Supporting evidence was also found in heritability tests involving these differences. The measurements of the infective larvæ presented by these authors, however, show some overlapping, and their heritability observations were carried only to the F ₁ generation. For these reasons a cytological examination was undertaken and studies of the chromosomes were made on aceto-orcein squashes of the gonads.