368 THE PROTOZOA 



irregular form, often seen in process of division. The parasite 

 grows, its nucleus multiplies, and it divides into a number of small 

 bodies, twelve to fifteen in number, each with one nucleus 

 (Fig. 156, L). During this process the leucocyte also increases 

 in size. Each of the small bodies produced by division grows 

 rapidly in its turn, and its nucleus divides repeatedly to produce a 

 very large number of nuclei, which become arranged in clumps 

 resembling the sporoblasts of a malarial parasite (Fig. 156, M 0). 

 Finally each mass becomes divided up into a great number of 

 minute " merozoites " of irregular form (Fig. 156, P R). During 

 this process the leucocyte first becomes greatly hypertrophied, and 

 finally breaks down altogether, setting free the merozoites, which 

 pass into the blood and attack the blood-corpuscles, into which they 

 penetrate and become the young halteridia (Fig. 156, A). The 

 development in the lung that has been described takes about 

 twelve days, so that the youngest parasites make their appearance 

 in the circulating blood about the twenty-sixth day after infection 

 by the fly. 



In the blood - corpuscles the youngest halteridia are minute 

 bodies with a single nucleus, which grow into the adult form, and 

 become male or female gametocytes, readily distinguishable by the 

 characters of the cytoplasm, which is darker in the female, and of 

 the nucleus, which is larger in the male (Fig. 156, B, C). No multi- 

 plication takes place in the red corpuscle : the sole multiplicative 

 stage known with certainty is that in the lung. Consequently, in 

 the pigeon the infection dies out after a time, unless re-infections 

 take place, and the degree to which parasites abound in the blood is 

 related directly to the number of infected flies fed on the bird. This 

 may not be equally true, however, of other species of these parasites. 



From Aragao's account it would appear that in H. columbce only male and 

 female halteridia (sporonts) occur. In other species, however, indifferent 

 forms occur also, which, it may be supposed, are destined as schizonts to 

 repeat the process of schizogony, and so to maintain the infection in the 

 bird, like the schizonts of the malarial parasites. Anschutz has described 

 in H. oryzivorce (of Padda oryzivora] a process of schizogony taking place in 

 the circulating blood. 



The development of the halteridia in the leucocytes may be considered, 

 probably, as equivalent to the schizogony of the malarial parasites. On this 

 interpretation the missing part of the development is that which corresponds 

 to the sporogony of the malarial parasite, and which in this case is either 

 suppressed entirely (" aposporogony," Aragao), or takes place in the verte- 

 brate host, in some manner yet to be described, instead of in the invertebrate. 

 The absence of sporogony, and of any but the sexual phases, in the Lynchia, 

 doubtless explains the short duration of the infectivity of the fly ; according 

 to Aragao, if the flies are fed for three days 011 clean pigeons, they cease to be 

 infective. Some of the stages in the lung show a certain resemblance to the 

 sporogony of the malarial parasites, especially the formation of sporoblast- 

 like masses, which, however, are probably more comparable to the schizonto- 

 cytes of Caryotropha than to true sporoblasts. 



