I'.H) 



PROTOZOA 



when the gametes are taken into the digestive tract of a blood-sucking mosquito. 

 The fertilized macrogamete, the ookinete, wanders into the intestinal wall, en- 

 larges enormously, encysts and produces numerous naked sporoblasts. Each 

 sporoblast gives rise to numerous sporozoites (u, 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 Anopheles will serve, not the more common Citlex. 

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

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

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

 by different parasites, the quartan fever being caused by Plasmodium (Hccma- 

 mceba malaria, pernicious malaria by P. prcecox. Allied to the Haemamcebas 

 and possibly also to the Trypanosomes, is Babesia (Piroplasma) bigemina, the 

 cause of Texas fever in cattle. The tick, Boophilus bovis, serves as the interme- 

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

 tion. Babesia bovis, intermediate host Ixodes rediwius, causes haemoglobinuria 

 in cattle. 



Order IV. Myxosporida. 



The Myxosporida (fig. 148) 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 organs like the heart, 

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

 closed in a membrane, and here they produce 

 the greatest injury. At first binucleate, they 

 soon become polynucleate, and apparently they 

 can reproduce by fission. Even before the 

 growth is ended they begin the process of sporu- 

 lation, hence the name 'neosporida.' Repro- 

 ductive bodies with one or two nuclei, the 

 anlagen of the pansporoblasts, are differentiated 

 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. 148, 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 early, but, 

 though long separated, they at last unite (II, 

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

 and protoplasm form the two-valved spore case, 

 and the remaining pair furnish the 'pole cap- 

 sules,' these being oval, and containing threads 

 which under proper conditions, are protruded 

 (III), the whole resembling a ccelenterate nettle 

 cell. The threads are for attaching the 'psoro- 

 sperms' (as the spores were formerly called). 



FIG. 148. Development of 

 Myxobolus pfeifferi, schematized 

 (after Keisselitz). 7, pansporo- 

 blast with envelope and residual 

 nuclei, r, divided into two sporo- 

 blasts; II, sporoblast developing 

 into spores; s, envelope cells; p, 

 pole cells with pole capsule; g, 

 amceboid germs with two nuclei ; 

 III, developed spore with ex- 

 truded threads of the pole cap- 

 sule, both nuclei of the amceboid 

 germs fused. 



The amceboid germs are set free, as experi- 

 ments on fishes show, by the digestive fluids, 



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



of spores differs with the species. 



