THE SPOROZOA 245 



and the merozoites are set free in the blood-plasma (Fig. 68, 10), 

 abandoning the residuary protoplasm, which becomes disintegrated, 

 scattering its contained pigment. The merozoites behave as did 

 the sporozoites from which they are descended ; that is to say, 

 they attack and penetrate fresh blood-corpuscles, and develop in 

 their turn into schizonts which produce fresh generations of mero- 

 zoites over again by the method of schizogony. 



The endogenous cycle is similar in all essential features in the three 

 species of the parasites of man, but each of them has its own distinctive 

 characteristics. The amoeboid movement is most active, and continues 

 longest, in Plasmodium vivax, most sluggish in P. malariae. In Laverania 

 the movements are very lively in the youngest, unpigmented stage. In 



Diagram of the complete life-cycle of the parasite of pernicious malaria, Laverania tnalariae, 

 Gr. et Fel. The stages on the upper side of the dotted line are those found in human blood ; 

 below the dotted line are seen the phases through which the parasite passes in the intermediate 

 host, the mosquito. I-V and 6-10 show the schizogony. VI-XII, the sexual generation, which 

 at VII splits into two lines (a) male and (b) female, to be united again by conjugation (XI 

 and XII). XIII, the motile zygote. XIV-XIX, sporogouy. I-III, young amoebulae in 

 blood-corpuscles, the two last showing the ring-form (which is, however, not quite correctly 

 drawn ; see p. 246). IV, older, actively amoeboid trophozoite. y, still older, less amoeboid 

 trophozoite. 0, mature schizont. 7, schizont with nucleus dividing up. 8, young rosette 

 stage. 9, fully -formed rosette stage; merozoites round a central residual mass of proto- 

 plasm containing the pigment, and blood - corpuscle beginning to break down. 10, mero- 

 zoites free in the blood by breaking down of the corpuscle. VI, young indifferent gametocyte. 

 Vila, male crescent. VII6, female crescent. VIII and b, the gametocytes becoming 

 oval. IX ft and b, spherical gametocytes ; in the male (IX a) the nucleus has divided up. 

 X a and b, formation of gametes ; in the male (X) the so-called flagella or male gametes (fl) 

 are thrown out, one of them is seen detached ; in the female (X6), a portion of the nucleus has 

 been thrown oiiu. XI, a male gamete penetrating a female gamete at a cone of reception formed 

 near the nucleus. XII, zygote with two pronuclei in proximity. XIII, zygote in the motile 

 stage (vermicule or ookinete). XIV, encysted zygote (oocyst). XV, commencing multiplication 

 of the nuclei in the oocyst. XVI, oocyst with numerous sporoblasts. XVII, commencing 

 formation of sporozoites ; the nucleus of each sporoblast has divided to form numerous nuclei, 

 each of which is growing out in a little tongue of protoplasm to become a sporozoite, but a few 

 nuclei remain behind as residual nuclei. XVIII, full-grown oocyst crammed with ripe sporo- 

 zoites; on one side the cyst has burst and the sj>oro7oites are escaping. XIX, free sporozoites, 

 showing their changes of form, n, nucleus of the parasite ; p, melanin pigment ; fl, " flagella " ; 

 sp.bl, sporoblasts ; r.n, residual nuclei ; r.p, residual protoplasm. (Chiefly after Neveu-Lemaire, 

 from whom the plan and arrangement of the different stages is borrowed, with slight modifica- 

 tions ; details of the figures arc founded on the figures of Grassi, Schaudinn (Leuckart's Zoolo- 

 gische Wandtafdri), Ross, and others.) 



all they slow down as the parasite approaches its full size. They differ 

 markedly also in their effects on the blood-corpuscle. Those attacked 

 by Plasmodium malariae diminish in size but retain their normal colour. 

 Corpuscles attacked by P. vivax, on the contrary, increase considerably in 

 size and become paler. The effect produced by Laverania varies greatly ; 

 the corpuscle is sometimes increased, sometimes diminished in size, and 

 the colour may be lessened or heightened in tint. 



Schaudinn [94] has recently studied the very active movements of 

 the sporozoites, and has observed the penetration of blood-corpuscles by 

 them, and by merozoites, in the case of the tertian parasite. He finds 

 that, as in the Coccidia, the sporozoites perform movements of flexion and 

 of peristaltic or euglenoid contraction, and that in addition they have the 

 power of gliding rapidly forward, with formation of a trail of gelatinous 

 substance. All three varieties of movement go on at the same time. The 

 penetration of the corpuscle takes about three-quarters of an hour, more 



