The objective was to study the chromosomes of Biomphalaria alexandrina snails (class Gastropoda) in control and infected state which could be helpful in understanding how host-parasite relationships in feasible and effective control measures. The chromosomal changes were studied using the air-drying method. The results showed that B. alexandrina had a diploid chromosome number, 2n = 36. Also, the meiotic stages were detected as early- leptotene and late leptotene, zygotene, diplotene, metaphase I. The result also revealed the presence of a primitive sperm, with a conical head and a very long, uni-flagellate tail. A comparative meiotic chromosome analysis between the control and infected ones showed some significant differences, as pachytene and diplotene were more condensed.