100 



rROTOZOA 



\Then the t^amctos are taken into the digestive tract of a blood-sucking mosquito. 

 The fertilized macroganiete, the ookiintc, wanders into the intestinal wall, en- 

 larges enormously, encysts and produces numerous naked sporohlasts. Each 

 sporoblast gives rise to numerous sporozoites (ii, 12) which wander into the 

 salivary glands of the mosquito (13) and are transferred to the blood of man by 

 the bite of the insect. For the transfer of human malaria apparently only 

 mosquitos of the genus Anoplnics will serve, not the more common Cuhw. 

 Since a temperature above 20° C. (68° F.) is best for the development of mos- 

 quitos, and water is necessarv for their development, the prevalence of malaria 

 in warm climates is easily understood. The ditTerent kinds of malaria are caused 

 bv different parasites, the quartan fever being caused hy PliisiiioJiidii (Hccma- 

 mccba nialaricc, pernicious malaria by P. prircox. Allied to the Ha?mama>ba; 

 and possibly also to the Trypanosomes, is Babesia {Piroplasma) hii^cuiina, the 

 cause of Texas fever in cattle. The tick, Boophiliis bovis, ser\es as the interme- 

 diate host, the parasites being passed by the eggs ('inherited') to the next genera- 

 tion. Babesia bovis, intermediate host Ixodes rediroiHS, causes hxmoglobinuria 

 in cattle. 



Order IV. Myxosporida. 



The ^Myxosporida (tig. 14S) are mostly large (sometimes visible to the naked 

 eye) and occur especially in fish and arthropods. \\ hen they occur in hollow 



organs they are naked and have pseudopodia, 

 but in parenchvmatous organs like the heart, 

 liver, brain, kidney, etc., they are usually en- 

 closed in a membrane, and here they produce 

 the greatest injurv. At first binucleate, thev 

 soon become polynucleate, and apparently they 

 can reproduce by fission. Even before the 

 growth is ended they begin the process of spioru- 

 lation, hence the name 'neosporida.' Repro- 

 ductive bodies with one or two nuclei, the 

 anlagen of the pa)isporoblasls. are dilTerentiated 

 in the protoplasm. In the best known forms 

 each pansporoblast gives rise to two spores. 

 By division there arise in all fourteen nuclei, 

 two of which (fig. 14S, r), with the surrounding 

 protoplasm, form the envelope of the pansporo- 

 blast. The others separate into two groups of 

 six each. One pair in each group with their 

 protoplasm form an 'amoeboid germ;' they ap- 

 pear to be separated from each other earlv, hut, 

 though long separated, they at last unite (II, 

 III, g), a case of caryoganiy. Two other nuclei 

 and protoplasm form the two-vahed spore case, 

 and the remaining pair furnish the 'pole cap- 

 sules,' these being o\al, and containing threads 

 which under proper conditions, are protruded 

 (III), the whole resembling a ca-lenterate nettle 

 cell. The threads are for attaching the 'psoro- 

 sperms' (as the spores were formerlv called). 

 The amoeboid germs are set free, as exjieri- 

 on fishc 



Fig. 14S. — nevclopment of 

 Myxohdhis pfciffcri, schenializcil 

 (after Kcisselitz). /, pans]ioro- 

 blast with envelope and residual 

 nuclei, r, divided into two sporo- 

 blasts; //, sporoblast developing 

 into spores; .?, envelope cells; /), 

 pole cells with jiolc capsule; !,', 

 amreboid germs with two nuclei; 

 ///, develojicd spore with ex- 

 truded threarls of the pole cap- 

 sule, both nuclei of the amceboid 

 germs fused. 



ments on fishes show, by the digestiAC fluids, 

 when they crawl into the tissues of the host. The number of pole capsules anci 

 of spores differs with the spiecies. 



