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what ruptures so many red blood cells all at one time 

 and produces the periodic chills and fever of malaria. 

 A loss of locomotor organs, and the development of 

 complex life cycles with incredible numbers of off- 

 spring, are common to the parasitic way of life. So 

 that sweeping all the odds and ends of protozoan 

 parasitism into one big hodgepodge and calling it the 

 Sporozoa does tidy up the rest of the protozoan clas- 

 sification, but it creates a group with members that 

 really have very little in common and that do not 

 represent a single branch of protozoan evolution. 

 The several subclasses of Sporozoa include many 

 important parasitic groups such as the myxosporid- 

 ians of fish disease, the microsporidians that kill 

 honeybees and silkworms and other higher inverte- 

 brates, and the haplosporidians that parasitize many 

 groups from rotifers to fish. Even the sarcosporidians, 

 which invade the muscle tissues of lizards, birds, and 

 also mammals, especially sheep, used to be placed 

 here. Now they are usually classed as fungi. Only 

 one of the subclasses, the Telosporidia, seems to be a 

 natural grouping of related orders, and as these 

 include many animals of importance to man they 

 will be briefly considered. 



THE GREGARINES 



The gregarines are mostly wormlike protozoans 

 that infest the digestive tracts and body cavities of 

 many invertebrates, but not of vertebrates. The 

 young form usually lives within a host cell, but as it 

 feeds and matures it protrudes from the cell, re- 

 maining attached only by the front end or leaving 

 altogether and moving about in the intestinal cavity 

 or one of the body spaces. Gregarines can be found 

 by teasing out on a microscope slide, and then dilut- 

 ing with water, the content or the lining of the in- 

 testine of a cricket or a grasshopper. It is likely one 

 will see the wormlike feeding stage gliding slowly 

 by means that are not evident, perhaps by slow 

 and inconspicuous muscular contractions. In this 

 group of gregarines the body is divided by a parti- 

 tion into a small front segment by which it can attach 

 to the host tissue, and a larger hind segment which 

 contains the nucleus. One may also see two individ- 

 uals attached end to end, the "gregarious" habit for 

 which the group is named. It is an indication that 

 sexual reproduction will ensue, with the front indi- 

 vidual as the female, the one at the rear as the male. 



THE COCCIDIANS 



The coccidians excite little notice as human para- 

 sites, though species of the genus Isospora are com- 

 moner in human feces than one would suspect from 

 the few cases of diarrhea actually reported. The bad 

 reputation of the group rests mostly on the damage 

 inflicted by Isospora, and more especially by the 

 genus Eiineiia, on domestic animals. Coccidiosis 



takes a heavy toll of chicken flocks and other poul- 

 try; and rabbits and cattle may also be .seriou.sly af- 

 fected, the latter having bloody feces, becoming ema- 

 ciated, and often dying. Practically any farm animal 

 may suffer from coccidian attacks, and so may dogs, 

 cats, and even canaries. In addition to these verte- 

 brate hosts, coccidians live in annelids, mollusks, and 

 arthropods. The feeding stage usually resides within 

 the lining cells of the intestine or of the organs that 

 connect with it, often the liver. The virulence of 

 many coccidial diseases is due to the tremendous 

 numbers of parasites that result from the multiple 

 fissions. 



<V- 



Cref^arina is a parasitic sporozoan likely to be foiiiicl 

 in the intestine of a grasshopper, cricket or cock- 

 roach. Pairs of cells often remain together, each one 

 subdivided into a small portion and a larger. In mat- 

 ing, the front individual will be the female, the rear 

 one the male. (General Biological Supply House, 

 Chicago ) 



THE HEMOSPORIDIANS 



The hemosporidians live within the blood corpus- 

 cles or other cells of the blood system of verte- 

 brates, and all of them require a blood-sucking inter- 

 mediate host during part of their very complex life 

 cycle. In human malaria, as everyone knows, the 

 intermediate host is a mosquito of certain species of 

 the genus Anopheles. For lack of this bit of knowl- 



[49 



