OTHER PROTOZOA 91 



gested ; the latter seem stimulated by the digestive juices to fur- 

 ther development. 



The macro gametocyte now goes through the process of matura- 

 tion (seep. 105), one small polar body being extruded (X, &.); 

 what remains is a large macrogamete. The nucleus of the micro- 

 gametocyte (IX, a. n.) divides into eight daughter nuclei which 

 migrate to the periphery and enter the long protoplasmic processes 

 that have, in the meantime, been thrust out from the cell (X, a.). 

 These flagelliform nucleated processes then break away from the 

 microgametocyte as male cells, microgametes or spermatozoa, 

 and move about until they encounter a macrogamete with which 

 they fuse (XI). What remains of the microgametocyte slowly 

 disintegrates. Only one microgamete fuses with a macrogamete 

 in the process of fertilization. 



The result of this fusion is a zygote which has been given the 

 name ookinet (XII) . This zygote becomes spindle-shaped (XIII) 

 and makes its way by vermiform movements to the epithelial cells 

 lining the alimentary canal of the mosquito; it penetrates these 

 and reaches the underlying tissues. Here it grows rapidly; 

 the nucleus divides, forming many daughter nuclei, and by the 

 sixth day as many cells are produced as there are nuclei (XIV- 

 XVI). Each cell is a sporoblast (XVI, Sp. bl.). The sporoblast 

 forms by division a number of germs, the sporozoites (XVII- 

 XVIII) ; these mature in about fourteen days and are then set 

 free into the body cavity of the mosquito (XVIII-XIX). From 

 here they are carried by the circulating plasma to all parts of the 

 body, finally collecting in the anterior region. They make their 

 way into the salivary glands, and are then ready to pass into the 

 blood of the human being at the time the mosquito makes its 

 next meal. 



Malarial fever is not present wherever Anopheles is found; for 

 example, Anopheles is common in England, but no malaria occurs 

 there. It is supposed that mosquitoes may become immune to 

 all kinds of blood parasites. A mosquito that is able to digest 

 the parasite becomes harmless to man. The mosquitoes of the 



