THE SPOROZOA 215 



progression within the host, until almost the entire epithelium of 

 the digestive tract may be destroyed. Sooner or later (in C. 

 schubergi after about five days) a limit is reached both of the 

 nutritive capacity of the host and of the reproductive power of the 

 parasite. Schizogony is then replaced by sporogony, a process 

 always initiated by the production of sexually differentiated con- 

 jugating individuals or gametes. Merozoites, descended from a long 

 succession of maiden schizonts, infect epithelial cells and become 



Fio. 51. 



The life-cycle of Coccidium schuleryi, Schaud. (par. Lithobivs forjhxttus), represented in all 

 its principal stages, combined into a single diagram, after Schaudinn [51]. I-IV represents 

 the schizogony, commencing with infection of an epithelial cell by a sporozoite or merozoite. 

 After stage IV the development may start again at stage I, as indicated by the arrows ; or it 

 may go on to the formation of gametocytes (V). V-VIII represent the sexual generation. The 

 line of development, hitherto single (I-IV), becomes split into two lines male (VI <5, VII <J, 

 VIII <J)and female (VI 9, VII 9, VIII 9), culminating in the highly differentiated gametes. 

 By conjugation these two lines are again united. IX, X show the formation of the zygote by 

 fusion of the nuclei of the gametes. XI-XV, sporogony. 



I, two epithelial cells showing the penetration of a merozoite and its growth into a 

 .schizont. Jl.C, host-cell; N, its nucleus; mz, merozoite. szt, schizont ; ky, its conspicuous 

 karyosome. II, the nucleus of the schizont is dividing up. Ill, schizont with numerous 

 daughter nuclei (n.ri), each with a conspicuous karyosome. IV, the schizont has segmented 

 into numerous merozoites (mz), each with a karyosome in its nucleus, implanted on a 

 central 7iiass of residual protoplasm, which in the ligure te hidden by the merozoites. V, a 

 host -cell containing two young gametocytes. The microgametocyte ((J) has tine granula- 

 tions ; the macrogametocyte (9) has coarse granules. VI 9, a host-cell containing an 

 immature female gametocyte (9 game), characteristically bean -shaped, with plastinoid 

 gr/mules (]>l.yr) in the cytoplasm, and a distinct karyosome (ky) in the nucleus. VII 9, a 

 .female gametocyte undergoing maturation, still in the host -cell. The body has become 

 spherical, the nucleus (n) irregular, and the karyosome has been expelled in fragments (ky). 

 VIII 9 , mature macrogamete, freed from the host-cell, and sending a cone of reception towards 

 an approaching microgamete (<$ gam). VI <$, a host-cell containing a full-grown micro- 

 gametocyte (($ yamc), spherical, with no plastinoid granules, and with distinct karyosome 

 (ky). Compare VI 9- VII <J, the nucleus of the microgametocyte has divided up to form a 

 great number of daughter nuclei (n.n), leaving the karyosome (ky) at the centre of the body. 

 VIII (J, the nuclei of the last stage have become microgametes ( gam), each with two flagella, 

 which are quitting the protoplasmic body of the gametocyte, and swimming to find a macro- 

 gamete. IX, the zygote surrounded by a tough membrane or oocyst (ode), and containing the 

 female chromatin, which is taking the form of a spindle (9), and the male chromatin in a 

 compact lump (). X, the chromatin from the two sources is spread over a spindle-like 

 figure (n.zyg), ami no longer distinguishable as male or female. XI, the spindle-shaped nucleus 

 of the zygote, having become compact (n.zyg), is dividing. XII, four daughter nuclei are 

 formed, the nuclei of the sporoblasts (n.sp.bl). XIII, the four sporoblasts are segmented off 

 from a small quantity of residual protoplasm, or "rdiquat kystal" (rp). Each sporoblast has 

 secreted a membrane, the sporocyst (sp.m). XIV, within each sporocyst the nucleus has 

 divided, and tlie protoplasm is segmented into two sporozoites (sp.z), and a reliquat sporal 

 (rp.sp). The reliquat kystal of the last stage is absorbed. XV, release of the sporozoites. An 

 aperture is formed in the wall of the oocyst (ode), and the sporozoites (sp.z) pass out through 

 it, having been liberated by bursting of the sporocysts (sp.m), which, with the reliquats sporaux 

 (rp.sp), are left behind in the oocyst. 



trophozoites in the usual way, but instead of growing rapidly into 

 ordinary schizonts like their parents, they grow much more slowly 

 to become the mother cells of gametes, or gametocytes. Since, further, 

 the gametes are differentiated into male elements or microgametes , 

 and female elements or macrogametes, their mother cells must be 

 distinguished further into microgametocytes and macrogametocytes, 

 which differ in all stages of their development. 



The microgametocytes are characterised by their dense, minutely - 

 reticular (alveolar) protoplasm, which is very finely and evenly 

 granulated, and is poor in larger enclosures or reserve material 

 (Fig. 51, VI (). When formation of microgametes commences, 

 the chromatin in the nucleus increases, fine granules of this sub- 



