302 ENTOMOLOGY 



investigators thought to be due to different species of para- 

 sites ; and when, as often happens, the malarial chill occurs 

 every day, this is attributed to two sets of tertian amcebulse, 

 sporulating on alternate days. 



After several successive asexual generations, there are pro- 

 duced merozoites which develop no longer into schizonts 

 but into sexual forms, or gametes. These occur in red 

 blood corpuscles either as macro gametes (female, 7, #) or as 

 microgametoblasts (male, ja, 8a), in which forms the parasite 

 is introduced into the stomach of a mosquito which has been 

 feeding upon the blood of a malarial patient. The macro- 

 gamete now leaves its blood corpuscle and becomes spherical 

 (p), as does also the microgametoblast (pa) ; but the latter puts 

 forth a definite number (six, in P. prcccox'yb) of flagella, 

 or microgametes, which separate off as motile male bodies, 

 capable of fertilizing the macrogametes. A microgamete 

 penetrates a macrogamete (10) and the nucleus of the one 

 unites with that of the other. The fertilized macrogamete now 

 becomes a migrating cell, or ookinete (n), which penetrates 

 almost through the wall of the stomach of the mosquito (12) 

 and then becomes a resting cell, or cyst. This oocyst (ij) 

 grows rapidly and its contents develop, by direct nuclear divis- 

 ion, into sporoblasts (14, 15), which differentiate into spindle- 

 shaped sporosoites (16, i). The sporozoites are liberated into 

 the body cavity of the mosquito, carried in the blood to the sali- 

 vary glands (as well as elsewhere) and thence along the hypo- 

 pharynx into the body of a human being, bird or other animal 

 attacked by the insect. 



The role of the mosquito as the intermediary host of mala- 

 rial organisms was discovered by Manson and Ross and con- 

 firmed by Koch, Sternberg and others. It has been found 

 repeatedly that certain mosquitoes (Anopheles) after feeding 

 on the blood of a malarial patient can transmit the disease by 

 means of their " bites " to healthy persons. Thus, Anopheles 

 mosquitoes were fed on the blood of malarial subjects in Rome 

 and then sent to London, where a son of Dr. Manson allowed 



