THE SPOROZOA 



251 



termed a vermicule by many writers (Fig. 68, XIII). Since it 

 corresponds exactly to the zygote of the Coccidia, but does not 

 form an oocyst immediately after fertilisation, Schaudinn has 

 proposed for it the name of ookinete, by which it is now generally 

 known. The movements of the ookinete are very similar to those 

 of a sporozoite, and consist of locomotion by gliding forwards, 

 combined with flexions and peristaltic contractions of the body 

 (Schaudinn [94a]). 



The ookinete by its own activity bores through the epithelial 

 lining of the stomach of the mosquito, and comes to rest in the 

 tissues immediately below the epithelium. Here it becomes rounded 

 off again in shape, and a delicate cyst-envelope of disputed origin 

 becomes formed round it (Fig. 68, XIV). The zygote is actively 

 parasitic upon its new host, and commences to grow considerably 

 in size, bulging out the stomach-wall towards the body-cavity. The 

 ookinete has now become the , 



oocyst ("spore-cyst," Lankes- 

 ter), differing from that of the 

 Coccidia in the thinness of 

 its envelope, which permits it 

 to absorb nutriment, like a 

 gregarine. Over 500 oocysts 

 have been found by Grassi in 

 the stomach-wall of a single 

 Anopheles mosquito. As the 

 oocyst grows, its nucleus, at 



first Single, divides tO form a ri dl >. ? f . s > oesophagus _; sit, .stomach ; cy, cysts ; Alt, 



number of daughter nuclei, 

 round each of which a small mass of protoplasm is centred (Fig. 68, 

 XV, XVI). The segments thus formed have received various names, 

 such as blastophores, zoidophores, or spore-mother-cells (Lankester), 

 but they are evidently comparable to the sporoblasts of Coccidia 

 and other Sporozoa, and may conveniently be designated as such. 

 The sporoblasts of the malarial parasites are irregular in form and 

 are not completely separated from one another, but remain in 

 connection by protoplasmic bridges. After formation of the 

 sporoblasts is complete a certain amount of residuary protoplasm 

 is left over, containing the melanin-granules originally present in 

 the gametocyte. 



In each sporoblast the single nucleus divides repeatedly to 

 form a great number of small daughter nuclei, which travel to the 

 periphery ; the surface of the sporoblast then grows out into a 

 number of slender protoplasmic processes, each of which takes one 

 of the daughter nuclei with it (Fig. 68, XVII). In this way 

 are formed a vast number of minute spindle-shaped sporozoites 

 ("blasts," "zoids," " exotospores "), each about 14 p. long by 1 //, 



int. 



Fio. 71. 



Stomach of a mosquito, with cysts of Haemosj 

 lia. oes, oesophagus ; st, stomach 

 Malpighian tubules; int, intestine. (After Koss.) 



