382 THE PROTOZOA 



individuals, would seem to indicate the existence of some form of 

 schizogony, yet to be discovered, in the tissues or internal organs 

 of the body. When the parasite or parasites have destroyed the 

 corpuscle in which they are lodged, they are set free in the blood- 

 plasma and penetrate other red corpuscles. 



Theileria parva stands apart from other piroplasms in its developmental 

 cycle in the vertebrate host. According to Gonder (738, 740), the minute 

 sporozoites injected by the tick collect in the spleen and lymphatic glands, 

 where they penetrate into lymphocytes, in which they grow rapidly. The 

 originally single nucleus divides repeatedly, and large multinucleate plasmo- 

 dial masses are formed which finally divide up into as many minute mero- 

 zoites, " agamonts," as there are nuclei ; the process recalls strongly the 

 schizogony of Hcemoproteus columbce (Fig. 157, K R), and leads to the break- 

 up of the lymphocyte. The first schizogonous generation may be repeated 

 several times, but at last a generation of " gamonts " is produced, which 

 are distinguished from the agamonts by characteristic differences in the 

 nuclear structure. The gamonts multiply by a process of schizogony, the 

 final or " gamogenous " generation, ending in the production of gametocytes, 

 minute parasites which do not multiply further, but penetrate into the red 

 blood- corpuscles, where they grow into adult gametocytes of two kinds male 

 gametocytes, which are long, slender, " bacillary " forms ; and female gameto- 

 cytes, which are plump, rounded, or pear-shaped forms. The gametocytes 

 can only develop further in 'the tick Rhipicephalus (see below). 



The forms found in the red corpuscles in the peripheral blood are either 

 gamonts or gametocytes, incapable of developing beyond the latter stage 

 except in the tick ; this explains a peculiarity of this parasite, namely, that 

 inoculation of infected blood into a healthy animal does not produce an 

 infection. 



The position of the genus Achromaticus, founded by Dionisi for A. vesperu- 

 ginis, parasitic in the blood of bats of the genus Vesperugo, is still doubtful. 

 It occurs under a number of different forms, some free in the blood- plasma ; 

 others, more common, within the corpuscles. The free forms are rounded or 

 spindle-shaped ; the intracorpuscular parasites may be also of these two 

 forms, but are more often pear-shaped. Within the corpuscles the rounded 

 and pear-shaped forms divide into two or four by a process of schizogony. 

 According to Gonder (737), the parasite has a double nucleus in all stages, 

 but this is not confirmed by Yakimoff and Co. (753), who regard the parasite 

 as a true Piroplasma. Neumann (745) states that in the bat- mite (Pteroptus 

 vespertilionis) the parasites undergo a transformation into flagellated organisms, 

 and considers Achromaticus allied to trypanosomes. It is not improbable 

 that stages of Achromaticus, both in the vertebrate and invertebrate hosts, 

 have been confused with stages of the trypanosome found in the blood of the 

 same vertebrate hosts. 



The process of division in Piroplasma canis (Fig. 161) has been studied in 

 great detail by Nuttall and Graham-Smith (748), and by Christophers (732). 

 The small rounded forms divide by simple binary fission of the ordinary type. 

 In the larger forms the division takes place in a peculiar manner, more akin 

 to gemmation than to ordinary fission. Before division the parasites become 

 amoeboid and irregular in form, and the nucleus has the form of a compact 

 mass. The nucleus then sends out two buds which grow towards the surface 

 of the body, and at this point two protoplasmic buds grow out into which 

 the nuclear buds pass. The buds increase in size until they become two pear- 

 shaped piroplasms, joined at their pointed ends by the continually- diminishing 

 remains of the body of the original parent- individual. The connecting mass 

 dwindles to a mere point, and finally the two daughter- individuals separate. 

 A modification of this method leads to the quadruple fission producing four 

 buds and four daughter-individuals, as in Babesia mutans. 



