ORDERS: MYCETOZOA AND AMCEBIDA 



173 



production of branching and anastomosing pseudopodia (Fig. 85). . At 

 certain stages, portions of the cytoplasm become encysted in resistant 

 capsules (sporangia), which may be arranged on stalks (Fig. 86). In this 

 respect there is a striking resemblance to fungi, to which group the 

 Mycetozoa were originally thought to belong. The sporangia eventually 

 rupture, and may liberate flagellated organisms which, after a free-living 

 existence, assume the amoeboid form. By growth, accompanied by 

 nuclear multiplication, the large plasmodia are produced. The Mycetozoa 

 are terrestrial in habit, and are commonly found 

 on the moist surfaces of decaying wood and leaves, 

 or in similar situations. Some of them may be 

 grown on the surface of agar plates. 



SYSTEMATIC DESCRIPTION OF THE ORDER 

 AMCEBIDA. 



From the point of view of parasitology it is 

 chiefly members of the order Amoebida which 

 have to be considered. The vast majority of the 

 Rhizopoda are free-living organisms, and only a 

 comparatively small number are truly parasitic 

 and adapted to their hosts in such a way that 

 a free extra-corporeal existence does not occur. 

 The fact that many of the free-living non-para- 

 sitic forms are able to produce protective cysts 

 of a resistant nature to enable them to withstand 

 desiccation has led to some confusion 

 encysted forms are frequently eaten accidentally 

 by human beings or animals, and may pass un- 

 harmed through the intestinal canal. After 

 escape from the body in the dejecta, they may find themselves in an 

 environment which is favourable for further development. The amoebae 

 emerge from the cysts, and by active multiplication increase enormously 

 in numbers in a comparatively short time. In this way, erroneous 

 impressions as to their parasitic nature may be obtained. Care must 

 always be exercised to guard against the possibility of confusing 

 these coprozoic forms with true parasites. In the case of true 

 parasites, the only forms which survive outside the body are, as a rule, 

 the encysted forms, which remain quite passive and unchanged till they 

 are ingested by another host. The unencysted stages are present in the 

 freshly passed stool, and show a degeneration which becomes more marked 

 as the interval since their escape from the body increases. The non- 



FiG. 86. — Badhaniia utri- 

 cularis. (After Lis- 

 ter, IN Lankester's 

 Treatise on Zoology, 

 1909.) 



Such «• Group of sporangia ( X 12). 



b. Cluster of spores (x 170). 



c. Single sjjore. 



d. Part of capillitium in in- 

 terior of sporangium (x 170). 



