IV. SPOROZOA: MYXOSPORIDA. 



217 



These division products are set free by a breaking down of the 

 corpuscle (period of chill) and infect other corpuscles. Thus 

 autoinfection can continue until at length sexual forms appear 

 ' spheres ' or macrogametes, flagellate microgametes incapable of 

 infecting the corpuscles. The conjugation of these seems to take 

 place when they are taken into the stomach of a blood-sucking 

 mosquito. After fertilization, the oosphere wanders into the 

 intestinal wall of the mosquito, grows larger, encysts, and produces 

 many sporoblasts, which in time form many sporozoites. These 

 migrate into the salivary glands of the mosquito and thence are 

 transferred to man with the sting of these insects. Since a tem- 

 perature above 20 C. (68 F.) is best for the development of the 

 stages in the mosquito, and since mosquitos need water for their 

 development, the prevalence of the disease in moist, warm regions 

 is easily understood. For the transfer of human malaria 'not all 

 mosquitos will serve, but apparently only those of the genus 

 Anopheles. The species of Culex convey bird malaria. The differ- 

 ent kinds of malaria seem to be produced by different parasites. 



Order IV. Myxosporida. 



The Myxosporida (fig. 158) are mostly large (sometimes visible 

 to the naked eye) and occur especially 

 in fish and arthropods. When they occur 

 in hollow organs they are naked and have 

 pseudopodia, but in parenchymatous or- 

 gans like the heart, liver, brain, kidney, 

 etc. , they are usually enclosed in a mem- 

 brane, and here they produce the great- 

 est injury. At first binucleate, they soon 

 become polynucleate, and it would appear 

 that they can reproduce by fission. Even 

 before the growth is ended they begin Flo 158 _ M 

 the process of sporulation. In the in- 

 terior single spherical protoplasmic bodies 

 separate, these having at first a single 

 nucleus, later more (as many as ten). 

 From each of these bodies arise from two 

 to many spores, the so-called psorosperms. These (fig. 158, 3) are 

 enclosed in a bivalve shell which includes, besides a binucleate 

 germ, one, two, or four polar capsules, these resembling somewhat 

 the nettle organs of the coelenterates. They are oval and contain 

 threads which, under certain conditions, are protruded (fig. 158, 2) 



MJIX- 



"* itAerkuhni ; fc, degen- 



eratmg nucleus; n, vacuole 

 formerly regarded as 



cleus; p, 



body, in 



threads. 



nu- 

 cnidocil-like pole 



s with exserted 



