(4) _Nicollia_ (Nuttall). Oval or pear-shaped parasites with characteristic nuclear dimorphism, and with quadruple division at first fan-like, then like a four-leaved clover. _N. quadrigemina_ from the gondi. (5) _Smithia_ (França). Pear-shaped, single forms stretching across the blood corpuscle. Multiplication into four in the form of a cross. _S. microti_ from _Microtus arvalis_, _S. talpæ_ from the mole. (6) _Rossiella_ (Nuttall). This belongs to the family Piroplasmidæ of França. It is intracorpuscular and non-pigment forming, occurring singly, in pairs, or occasionally in fours. It is usually round and larger than Babesia. The parasite multiplies by binary fission. _R. rossi_ in the jackal. The genus _Babesia_ is the best known and most important, and will be considered next. Genus. *Babesia*, Starcovici, 1893. Syn.: _Pyrosoma_, Smith and Kilborne, 1893; _Apiosoma_, Wandolleck, 1895; _Piroplasma_, W. H. Patton, 1895; _Amœbosporidium_, Bonome, 1895. The organisms belonging to this genus are pyriform, round or amœboid. The characteristic mode of division is as follows: Just before division the parasite becomes amœboid and irregular in shape, (fig. 91, _1–5_) with a compact nucleus. The latter gives off a nuclear bud. This nuclear bud divides into two by forking (fig. 91, _6_, _7_). The chromatin forks grow towards the surface of the body of the rounded parasite, and then two cytoplasmic buds grow out. The forking nuclear buds, which are *Y*-shaped, pass into the cytoplasmic outgrowths[212] (fig. 91, _8_, _9_). The buds gradually increase in size at the expense of the parent form until they become two pear-shaped parasites joined at their pointed ends. The connecting strand shrinks and the two daughter forms separate (fig. 91, _10–14_). The pyriform parasites after having exhausted the blood corpuscle escape from it (fig. 91, _15_), and seek out fresh host corpuscles, entering by the rounded, blunt end (fig. 91, _1_). It is the pyriform phase of the parasite which penetrates red blood corpuscles, not rounded forms, which die if set free. The pyriform parasite, however, becomes rounded (fig. 91, _2_, _3_), soon after its entry into a fresh host cell. This interesting mode of division by gemmation and chromatin forking has been made diagnostic of the genus _Babesia_ by Nuttall.[213] Rounded forms of _Babesia_ divide by binary fission, and this direct method can also be adopted by the other forms of Babesia. [212] Nuttall and Graham-Smith, _Journ. Hyg._, vii, p. 232. [213] “Piroplasmosis,” Herter Lectures, _Parasitology_, vi, p. 302. [Illustration: FIG. 91.--_Babesia_ (_Piroplasma_) _canis_, life-cycle in stained preparations of infected blood of dog. (After Nuttall and Graham-Smith.)]