78 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



usually situated near the blunter end of the parasite, and from it arises 

 a terminal flagellum. A Crithidia is an organism very much resembling 

 a Herpetomonas, with a pear-shaped body and, sometimes, a rudimentary 

 undulating membrane. A Trypanosoma is an elongated parasite which 

 has a nucleus, a kinetonucleus, an undulating membrane and a flagellum. 

 Species of Herpetomonas, Crithidia and Trypanosoma are frequently 

 found in the intestines of insects. One species of Herpetomonas is a 

 frequent and harmless parasite in the intestine of the house fly. The 

 genus Trypanoplasma contains organisms which have a flagellum at either 

 end, as well as an undulating membrane. They are parasitic in the blood 

 of fishes. The genera Cercomonas, Monas, and Plagiomonas include 

 small, unimportant flagellate organisms which have been found, occa- 

 sionally, to be parasitic in man; they have been found in the urine, and 

 in necrotic material from the lungs. A Trichomonas is a pear-shaped 

 organism which has four flagella attached to its blunt end, and an undu- 

 lating membrane. A species of it is sometimes found in the human 

 bladder. Other species are common, usually harmless, parasites in the 

 intestines of pigs, frogs and other animals. The most important species 

 of the genus Lamblia is Lamblia intestinalis. It also is a pear-shaped 

 organism. It has several flagella and is distinguished by possessing a 

 depressed sucker, by which it attaches itself to the wall of the intestine of 

 the animal in which it lives. It may cause severe diarrhoea in man, and 

 it may produce a fatal disease of the intestines in rabbits. 



The SPOROZOA are protozoa which may multiply by the production 

 of spores; they are always parasitic at some stage of their life cycle. There 

 are very many sporozoa so, for convenience of classification, they are sub- 

 divided into seven orders. The GregarincB have a very distinctive 

 shape; the single cell, which composes them, is divided into two or more 

 divisions. The first of these divisions is furnished with hooks through 

 which the parasite attaches itself to its host. None of the gregarines are 

 parasitic on mammals ; worms are the hosts for some of them. The Coccidia 

 are usually parasitic within cells of their host, other than blood cells; for 

 example, Coccidium cuniculi (p. 68 1) enters the liver cells of the rabbit, 

 while Coccidium avium enters and destroys the cells lining the intestines 

 of the birds which it infects (p. 681). The Hamosporidia live, for a part 

 of their life cycle, within the red cells of the blood of their hosts. They 

 are a very important order. The genus Plasmodium causes malaria in 

 man (p. 682); while Proteosoma and Hamoproteus are malarial parasites 



