52 



COLLEGE ZOOLOGY 



trophozoites come together and are sur- 

 rounded by a cyst wall. Each then divides, 

 producing a number of small cells called 

 gametes. The gametes unite in pairs to form 

 zygotes. It is probable that the gametes 

 produced by one of the trophozoites do not 

 fuse with each other but with gametes pro- 

 duced by the other trophozoite enclosed in 

 the same cyst. Each zygote becomes lemon- 

 shaped and secretes a thin hard wall about 

 itself. It is now known as a spore. The 

 nucleus of the spore divides successively into 



2,4, and finally 8 daughter nuclei, each of 

 which, together with a portion of the cyto- 

 plasm, becomes a sporozoite. 



OTHER SPOROZOA 



Four subclasses and five orders of Sporo- 

 zoa are usually recognized by zoologists. 

 Some of the species of great importance to 

 man are described in Chapter 7. Two types 

 that are easily obtained for study are greg- 

 arines and coccidians. 



OJI 



ORDER HAEMOSPORIDIA 

 Sporozoite of Lankesferella 

 in frog erythrocyte 



ORDER COCCIDIA 

 Oocyst of Isospora 

 hominis from human 

 intestine 



ORDER 

 MICROSPORIDIA 

 Spores of Thelohania 

 coniejeani from cray- 

 fish muscle 



ORDER GREGARINIDA 

 Two trophozoites (attached 

 end to end) of Gregarina 

 blatiarum from cockroach 

 intestine 



ORDER HAEMOSPORIDIA 

 Gametocyte of Hoemoprofeus 

 in bird erythrocyte 



Figure 24. Types of sporozoa. 



Gregarines may be obtained from the in- 

 testines of grasshoppers, cockroaches, and 

 meal worms. Spores are swallowed by these 

 insects from which sporozoites escape. These 

 penetrate the cells of the intestinal wall, and 

 trophozoites develop from them. The 

 trophozoites, after undergoing a period of 

 growth, break out into the intestine, where 

 they unite end to end (Fig. 24) . The rest of 

 the life cycle is similar to that of Monocystis. 



Coccidia are most easily obtained for 

 study from the rabbit. Oocysts may be found 

 in the feces of a large proportion of these 



animals. They consist of a single cell when 

 passed, but if the material is placed in a 5 

 per cent aqueous solution of potassium di- 

 chromate to inhibit the growth of bacteria, 

 four spores, each containing two sporozoites, 

 will develop within each cyst in about three 

 days. 



ORIGIN OF THE SPOROZOA 



Parasitic protozoans, no doubt, evolved 

 from free-living species or from other para- 



