On the Parasitic Development of Monodontus Trigonocephalus, the Sheep Hookworm

Abstract

A certain amount of confusion still exists as to the terminology to be adopted in discussing the various stages in the life cycle of the nematoda. This appears to be largely due to a difference of opinion as to the termination of each stage.After a larva has reached a certain size, it commences to change in form and completes this process by shedding its cuticle. This change in form is the lethargus. It may or may not immediately escape from the cast cuticle, but when it does, the ecdysis is complete. The form which emerges is morphologically identical with the form inside the cuticle after the completion of the lethargus.This accordingly gives a double choice as to the exact end of the stage. It may be during the lethargus, when the morphology of the form is changing, or it may be at the moment when the larva leaves the cast cuticle. The interval between these periods is slight in some cases but is considerable in the case of the infective stage. As the physiological end of the stage seems to coincide with the lethargus, I have accordingly based my nomenclature on it.