THE H.EMOSPORLDIA 367 



provided with wings (some genera of this family, such as Melophagus, 

 the common sheep-ked, are wingless), are extremely louse-like in 

 appearance, and creep in the plumage of birds ; they attack nest- 

 lings as well as adults a fact which explains the appearance of the 

 infection in pigeons before they have left the nest. 



When blood containing the parasites is taken up by a Lynchia, 

 the ripe gametocytes burst the corpuscles in which they are con- 

 tained, round themselves off, and form gametes, in the manner 

 already described for haemamcebee, in the stomach of the fly 

 (Fig. 157, D, E). Fertilization then takes place, and ookinetes are 

 formed (Fig. 157, F J). Practically the only difference from the 

 hseniamoebae is that the ookinetes get rid of their melanin-pigment, 

 which is cast off in a small bead of protoplasm at the hinder end. 



The ookinete grows considerably larger than the full-grown 

 halteridia of the blood. The development of the parasite does not 

 proceed further, apparently, than this stage in the fly, and it is the 

 ookinete which is inoculated back into the bird's blood by the 

 Lynchia. 



At this point there is a gap in the development which it remains 

 for further observations to fill up. Thirteen or fourteen days after 

 the actual infection by the fly the parasite makes its first recorded 

 appearance in the pigeon, within, a leucocyte which is adherent to 

 the wall of a blood-capillary, so that possibly the previous develop- 

 ment of the parasite has taken place in an endothelial cell (Aragao). 

 The parasite has the form of a small round body contained in the 

 cytoplasm of a leucocyte (Fig. 156, K) ; it has a single nucleus of 



FIG. 157. Developmental cycle of Hcemoproteus columbce, after Aragao (683). 

 A, Youngest halteridia in the blood-corpuscles: a, female; b, male; B, C, 

 growth of the gametocytes, female (a) and male (b) ; D, gamete-formation : 

 a, reducing division in the female gametocyte ; b, division of the nucleus of 

 the male; E, ripe gametes: a, female; b, male (" Polymitus " stage); F, 

 copulation of male and female gametes ; G, the zygote beginning to assume 

 the ookinete-form ; //, the oiJkinete with pigment in the body ; /, the pigment 

 passing to the hinder end of the body ; J, the ookinete after it has got rid of 

 the pigment. 



K, Youngest stage in the leucocyte in the lung of the pigeon ; L, the pre- 

 ceding stage has divided into a number of small individuals, each with one 

 nucleus, and the leucocyte has increased in size ; M, the individuals of the 

 last stage have grown in size and become multinucleate ; the leucocyte still 

 further enlarged ; N, further advance on the last ; O, the greatly hypertrophied 

 leucocyte contains a number of multinucleate masses ; P, Q, further multi- 

 plication of the nuclei ; the leucocyte beginning to break down ; R, the multi- 

 nucleate masses become divided into a vast number of small uninucleate 

 individuals, which are set free from the leucocyte by its disintegration, and 

 which penetrate into blood-corpuscles and there become the youngest halteri- 

 dia, as in A. 



The stages D J are passed through in the fly (Lynchia), the^ stages K0 

 in the pigeon. Between J, the last stage seen in the fly, and K, the earliest 

 stage yet found in the pigeon, is a gap which it remains for further investigation 

 to fill. 



The stages H J are drawn rather too small in proportion to those pre- 

 ceding. 



