214 HANDBOOK OF PROTOZOOLOGY 



was established by Casagrandi and Barbagallo who did not 

 know the existence of the genus Endamoeba. The nucleus has 

 the following characteristics: Vesicular; nuclear membrane is 

 thin, but distinct. A comparatively small endosome is located 

 in or near the center and there are varying numbers of peripheral 

 chromatin granules free or attached to the nuclear wall. 

 Numerous species in man, mammals, and invertebrates. A 

 number of authors hold that there is not a sufficient difference 

 between the genera Endamoeba and Entamoeba to justify 

 their generic separation, and so combine them. 



A. Entamoebae of man 



Entamoeba histolytica Schaudinn (Fig. 85, a-f). The amoeba 

 is small and measures 20 to 30 microns in diameter. Its cyto- 

 plasm is usually differentiated distinctly. Large lobopodia are 

 often formed in an explosive manner, and are composed ex- 

 clusively of ectoplasm. The endoplasm contains a single vesicu- 

 lar nucleus which appears in life as a ring and food vacuoles 

 containing erythrocytes, tissue cells, leucocytes, etc., of the 

 host in variable number. The typical nucleus shows upon 

 staining the following parts: a nuclear membrane, peripheral 

 chromatin granules, a centrally located small endosome rich in 

 chromatin material surrounded by a clear ring and an indistinct 

 achromatic network with a few scattered chromatin granules. 

 This amoeba invades the tissues of the gut-wall and multiply 

 by binary fission. Under certain circumstances not well under- 

 stood, the active trophozoite extrudes its undigested food 

 material and decreases in size, possibly by division also. Such a 

 form is sluggish and shows frequently glycogen bodies and 

 elongated refractile bodies which stain deeply with a nuclear 

 stain (hence called the chromatoid bodies). This phase is 

 known as the precystic stage. The cyst is formed when the pre- 

 cystic stage ceases to move and becomes surrounded by a 

 definite cyst-membrane. The cyst measures 5 to 20 microns in 

 diameter. At first it contains a single nucleus which divides 

 later twice and tetranucleate cyst is formed. The glycogen and 

 chromatoid bodies become absorbed, as the cyst grows older. 

 The changes between the cyst and the young trophozoite are 

 not known, although in recent years numerous investigators 



