Preparasitic Moults in Nippostrongylus Muris, with Remarks on the Structure of the Cuticula of Trichostrongyles

Abstract

Rhabditiform first-stage larvae of Nippostrongylus muris are about 270–550μ long. The development of these larvae culminates in a moult, which occurred 36–48 hours after cultures were prepared. The first moult is preceded by an unusually early separation of the first cuticle, which is fine and unstriated, from the body tissue in the tail region and, later, by the formation of an underlying new cuticle, which is thicker and prominently striated.Early second-stage rhabditiform larvae differ in certain morphological respects from first-stage larvae. Second-stage larvae are about 470–750μ long.A second preparasitic ecdysis occurs and the infective larva is a true third-stage larva. This moult was the only one previously known to occur during the preparasitic development of N. muris.The post-cervical cuticular inflation in N. muris is regarded, on the basis of a comparative study of the cuticle of this species and of Haemonchus contortus and other trichostrongyles, as resulting from the separation of the second and third layers of the cuticle. Yokogawa's view that Nippostrongylus muris has two cuticulae is rejected. N. muris has a single cuticula, apparently made up of four layers.N. muris undergoes four complete moults and the development of this species does not differ in any essential respect from that reported for other strongyles.