138 



AMEBiE 



and it is not improbable tliat they will prove to be of wide geo- 

 grapliic distribution, and often mistaken for Endamceba or flagel- 

 lates, according to the phase of existence in which they are observed. 

 The Parasites. — As already remarked, Craigia resembles 

 some of the free-living soil amebse in that it passes through a 

 flagellated stage, but it differs from them in having only a single 

 flagellum instead of two. Briefly the life history of Craigia 

 hominis (Fig. 40A to F) is as follows: the adult form (Fig. 40E), 

 resembling a typical ameba, is about half the size of the dysentery 



G n 



Fu;. 40. Life f-yclcs of Craigia. 



C. hominis (A to F). A, swarmer ju.st escaped from cyst; B, young flagellatfd 

 form; C, mature flagellated form; D, same, dividing; E, amebic form before 

 encystment; F, cyst with swarmers. 



C. niigrans (G to L). G, swarmer just escaped from cyst; H, young flagellated 

 foim; /, mature flagellated form; J, amebic form developed by transformation 

 from I, without any nuiltiplication; K, mature amebic form, ready to encyst; L, 

 cyst with swarmers (note larger size and smaller number of swarmers than in C. 

 hominis). X 1000. (After Barlow.) 



ameba (10 to 25 n dry^ij to y^V^ oi an inch) in diameter), and 

 when moving exserts several l)lunt pseudopodia. In addition 

 to the nucleus it possesses a structure, possibly a parabasal body, 

 which appears as a bright glistening object in the living animal 

 and stains deeply with nuclear stains. The animal multiplies 

 by .simple division for a time, but eveiituall}' encysts, rotating 

 on its axis during the process of forming the double-walled cj'st. 

 When fully developed the cysts (Fig. 40F) are considerably 

 larger than those of the ch'senterj^ ameba (15 n (tbVtj of an inch) 

 in diameter) and contain al)Out 40 round refractive bodies, which 



