Abstract
The developmental features, growth and organogenesis of Macroorchis spinulosus were observed in albino rats. Globular and thick walled metacercariae, possessed a stylet, Y-shaped excretory bladder and extracecal testes. In albino rats, M. spinulosus showed habitat shifting. The majority of M. spinulosus reside in the jejunum for the first four days post infection (p.i.) and migrate to the duodenum at the later stage of infection. M. spinulosus grew rapidly during the first four days and reached full maturity at 14 days p.i. and later reduced in size. The ovary was separated from the genital primodium at one day p.i. The seminal vesicle appeared on the third day and divided into two sacs on the fourth day p.i. and intrauterine eggs and sperm mass were produced on the fourth day. Organogenesis and enlargement of reproductive organs governed the growth of M. spinulosus. The similarity of related species of the genus Macroorchis to M. spinulosus was discussed in consideration to developmental features.