ABSTRACT. Studies were made on the development of Babesia gibsoni in the midgut of the larval tick, Rhipicephalus sanguineus. Six hr after repletion, merozoites of B. gibsoni, freed from erythrocytes, were observed in the midgut contents of the tick. After that, within 24 hr, those merozoites were transformed into the ring-forms which were relatively large, 2-3 µm in diameter. Later, the ring forms developed into the spherical forms which were subelliptical in shape and 4-6 µm in diameter. Within 2-4 days, the elongated forms, 5-8 µm in length, were found. At this time, some of the binucleated fusion form has assumed a form intermediate between the spherical and elongated-forms. About 5-6 days after repletion, large round or elliptic zygotes, 8-10 µm in diameter, were observed in the tick gut.-KEY WORDS: Babesia gibsoni, development , Rhipicephalus sanguineus.

ABSTRACT. Studies were made on the development of Babesia gibsoni in the midgut of the nymphal stage of the tick, Rhipicephalus sanguineus. Six hr after repletion, merozoites of B. gibsoni, free of erythrocytes, were observed in the midgut contents of the ticks. After that, within 24 hr, those merozoites were transformed into ring-forms which were relatively large ring 1-2 µm in diameter. Later, the ring forms developed into spherical forms which were somewhat elliptical in shape and 3-4 µm in diameter. Within 2-4 days, bizarre forms (5-6 µm in diamater) developed into elongated forms (5-6 µm in length). About 5-6 days after repletion, large round or elliptic zygotes (7-9 µm in diameter) were observed in the ticks gut.-KEY WORDS: Babesia gibsoni, development , Rhipicephalus sanguineus.

There are many reports on the development of Babesia species in the host and the vector ticks [1,2 ,9 ,11,15]. However, no detailed observations on the developmental stages of Babesia ovata [12] in Haemaphysalis longicornis have been made yet. Babesia species are known to undergo morphological change during the growth in the host and the vector ticks. The present was carried out to study the growth of B. ovata in periphelal blood of host cattle, in the midgut, haemolymph and eggs of the tick, H. longicornis.