THE H^MOSPORIDIA 363 



gnat's stomach, and comes to rest in the subepithelial tissue ; here 

 it rounds itself off and forms an oocyst (Fig. 156, XIV.), becoming 

 surrounded by a delicate membrane, which is not, however, of a 

 tough and impervious naturelike a coccidian oocyst, since the parasite 

 continues to absorb nutriment and to grow in size, bulging out the 

 stomach-wall towards the body-cavity. As it grows, the originally 

 single nucleus of the zygote multiplies by binary fission, and the 

 cytoplasm becomes concentrated round each nucleus to form a 

 " sporoblast," so called (Fig. 156, XV., XVI.). In each sporoblast 

 the nucleus divides repeatedly, and then the surface of the sporo- 

 blast grows out into slender tongue-like processes, each carrying 

 out one of the nuclei in it (Fig. 156, XVII.). Thus a vast number 

 of minute sporozoites are formed by a process of multiplication 

 recalling that seen in the schizogony of Aggregate or Porospora. 

 Finally the cyst contains some hundreds, or even thousands, of 

 sporozoites, together with a certain amount of residual protoplasm, 

 in which the melanin-pigment of the macrogamete is contained 

 (Fig. 156, XVIII.). The ripe cysts burst and scatter their contents 

 in the body-cavity (haemocoele) of the mosquito ; the sporozoites 

 pass by means of the blood-currents to the salivary glands, in 

 which they collect in vast numbers. The mosquito is now infective ; 

 at its next feed, which is usually the fourth, counting as the first 

 that by which it first took up the parasites in the infected blood, 

 the tiny sporozoites pass with the salivary secretion down the 

 proboscis into the blood of the man on whom the mosquite feeds, 

 and so produce a new infection. 



A disputed point in the life- cycle is the manner in which relapses are brought 

 about in malarious persons ; as is well known, persons who have had malaria 

 may have fresh attacks of the disease under conditions which preclude infec- 

 tion by mosquitoes, and leave no doubt but that the parasite has been present 

 in the body in a latent or inconspicuous condition, and has for some reason 

 reacquired the power of multiplication until its presence becomes perceptible 

 again. Two views have been put forward to explain relapses. According 

 to Schaudinn (130), in the healthy intervals all forms of the parasite have 

 died off except the female sporonts, which are the most resistant forms of the 

 parasite, and maintain their existence in a resting state ; when, however, the 

 conditions occur, whatever they may be, which favour a relapse, the female 

 sporonts multiply parthenogenetically (Fig. 72, p. 137), and produce a brood 

 of merozoites which are the starting-point of a fresh series of schizogonous 

 generations. Ross, on the other hand, believes that in the healthy intervals 

 the number of parasites in the blood merely falls below that sufficient to pro- 

 duce febrile symptoms, and that a relapse is brought about simply by an 

 increase in the numbers of the parasites present. 



The number of cysts formed in the stomach of the mosquito may be very 

 large, 500 or more ; and the cysts themselves vary in size considerably, some 

 developing only a few hundreds of sporozoites, while in others they are to be 

 counted in thousands. Even in mosquitoes of a species susceptible generally 

 to a particular species of malarial parasite, however, the sporonts do not 

 succeed in every case in passing through their sexual stages and developing 

 normally (compare Darling, 669). In many cases also the cysts degenerate 



