GENERA: AMCEBA AND HARTMANNELLA 175 



Family: AMCEBID^ Bronil, 1859. 

 In this family are included a number of free-living amoebao, and most 

 of the parasitic forms which occur in the intestine of man and animals. 

 Not many years ago all amoebae, including the parasitic forms, were 

 placed in the genus Amceha. It is now recognized that several distinct 

 genera are represented, but the group has not been sufficiently studied 

 to enable precise definitions to be given. Many of the smaller free-living 

 forms which were grouped under the name Amceha Umax have been placed 

 in the genera Hartmannella, Sappinia, Vahlkampfia, which can be identi- 

 fied by the type of nuclear division and other details, while the parasitic 

 amoebae have been separated into the genera Entamceha, Endamceha, 

 lodamceba, Endolimax, and Dientamceha. The exact limits of the genus 

 Amoeba are doubtful, but the majority of the large free-living uninucleated 

 forms, such as Amoeba proteus and Amoeba verrucosa, which may have 

 a diameter of 500 microns or more, are regarded as belonging to it. Much 

 more information regarding the complete life-histories, the methods of 

 reproduction and encystment, and the details of nuclear division, are 

 required before the group can be satisfactorily defined. 



Oemis : Amoeba Bory, 1822. 

 In this genus are included the vast majority of free-living amoebae. 

 In most cases they are placed in the genus because detailed informa- 

 tion regarding their structure and development is wanting. It seems 

 probable that future investigators will show that the only ones which 

 actually belong to it are the large free-living forms like Amoeba proteus, 

 Amoeba verrucosa. Amoeba vespertilionis, and Amoeba hydroxena described 

 by Entz (1912) as parasitic on Hydra oligactis. 



Genus: Hartmannella Alexeieff, 1912. 



The amoebae belonging to this genus are recognized by the character 

 of their nuclei and method of nuclear division. The nucleus is spherical, 

 has a large central karyosome, and peripheral chromatin in the form of 

 granules either on the inner surface of the nuclear membrane or in the 

 space between the membrane and karyosome. During division the 

 karyosome disintegrates, and a spindle is formed upon which definite 

 chromosomes become arranged as an equatorial plate (Fig. 88). The 

 nuclear membrane usually disappears at some stage of the division. The 

 cysts are spherical structures. The numerous species belonging to this 

 genus are distinguished by the details of nuclear division and the character 

 of the cysts. 



Hartmannella hyalina (Dangeard, 1900).^ — This amoeba, which is often 

 found in stale fa>ces or in agar plate cultures made from dirty water, 



