Haemonchus contortus, otherwise known as the “Barber Pole Worm”, “The Wire Worm” or simply as the large stomach worm of sheep, has been the subject of much scientific interest for the past quarter of a century. Considerable work has been done which has established this parasite as a factor of economic importance and its presence as a pathological agent in the abomasum of ruminants is generally well recognized. This worm is one of the largest of the Strongyloid group, measuring sometimes an inch in the females and three-quarters inch in the males, and its general anatomy is fairly well known. The literature does not, however, reveal any work which has been done in connection with the development of the reproductive cells of this species. In the present work a study has been made of spermatogenesis and oogenesis with some attention directed to methods of copulation, the passage of the sperm cells upon entrance into the vulva and the anatomical location in the female where the sperms are collected for the purpose of fertilization of the ova. No histologic section, depicting the entrance of the sperm into the ova, has been observed but the developmental stages immediately following this penetration of the ova are shown in this paper. Even though a considerable amount of material has been examined which has afforded opportunity for studying the entire reproductive organs of both male and female worms, several developmental stages which have been reported as occurring in nematodes, have not been observed in this study. Sufficient evidence, however, is herein presented which indicated very clearly and definitely the normal chromosome number. / Master of Science