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948 locomotion. The development in the vertebrate host appears to proceed solely by either binary or quadruple fission.

The transmission of the piroplasms is effected by ticks; in the case of P. bovis it is adapted to the life-history of the transmitting tick (Ixodes reduvius or Magaropus australis), and in P. canis to Rhicephalus sanguineus. The tick is hatched first as a minute six-legged larva, which becomes an eight-legged nymph, differing from the adult only in the absence of genital organs. In each stage the tick feeds but once. The infection is passed to the ova by the infected female tick. The developmental stages of this parasite in the tick are little known; apparently, according to Christophers and Koch, the parasites escape from their red cells and become transformed into starshaped bodies representing the gametocytes. Conjugation of these bodies takes place, and when complete the zygote becomes a motile body resembling an oökinete. The oökinetes apparently penetrate into the ova of the tick, when they

Fig. 254.—Developmental forms of Piroplasma canis in tick's gut. (After Koch, Klein, and Christophers.)

assume a globular shape. When the egg hatches into a six-legged larva these bodies break up into a number of sporoblasts, which become scattered throughout its tissues. The sporoblasts divide in turn into a number of sporozoites resembling the pear-shaped forms seen in the blood; these, according to Christophers and Gonder, contrive to enter the salivary glands, and thus re-enter the blood-stream when the tick becomes adult and again feeds on blood. (Fig. 254.)

Parasites belonging to this order are developed from small amœbulæ within the body of the one host. No definitive host is known. The adult parasite is a large cyst contained within a definite membrane and incapable of independent movement. The motile amœbula is followed by a plasmodial intracellular stage in which spore formation is commenced and is continued throughout the life of the parasite. The order is divided into two suborders: (1) the Cnidosporidia, characterized by the possession of polar capsules, and pear-shaped bodies provided with a spiral and delicate filament; (2) the Haptosporidia, in which those features are absent.