15 



IV. 



THE GENERA OF AMOEBAE LIVING IN MAN. 



All the older writers who dealt with the amoebae of man placed them 

 in the genus Amoeba, which originally included a very heterogeneous 

 collection of naked rhizopods. As knowledge accumulated, however, it 

 became clear that this genus would have to be dismembered ; and one 

 of the earliest attempts in this direction was made by Leidy (1879), who 

 proposed to separate the amoeba parasitic in the cockroach (Atiioeba 

 blattac Biitschli) from the free-living forms. For this organism he 

 proposed the new genus Endamoeba* Consequently, the type species 

 of Endamoeba Leidy is E. blattae Biitschli. 



Casagrandi and Barbagallo (1895 a), apparently in ignorance of Leidy's 

 work, proposed a new genus Entamoeba for the amoebae which they 

 studied from man. At first (1895 a) they called their organism Entamoeba 

 colt, believing it to be the same as that described by Losch (1875) and 

 called by him " Amoeba coli " ; but they renamed it later Entamoeba 

 liominis (Casagrandi and Barbagallo, 1897). 



It is clear from their papers that the actual organism to which these 

 names were applied was the large harmless amoeba of the human colon 

 — now generally known, since the time of Schaudinn (1903), as Ent- 

 amoeba coli. It follows that the type species of the genus Entamoeba 

 Casagrandi et Barbagallo is E. coli. 



The genus Entamoeba of Casagrandi and Barbagallo was accepted by 

 Schaudinn (1903) for E. coli and also for E. histolytica, the dysentery 

 amoeba : and since the appearance of his work it has been customary to 

 refer almost all the parasitic amoebae to this genus. A curious belief 

 seems, indeed, to have grown up that there are but two genera of 

 amoebae — free-living species all belonging to the genus Amoeba, and 

 parasitic forms all belonging to Entamoeba. Walker (1911, 1913), for 

 example, in his admirable works on the amoebae of man, speaks as 

 though no other genera exist ; and most medical writers who have 

 studied amoebae apparently share this belief. No zoologist, however, 

 can now hold such a view for a moment ; for it is certain that, from the 

 zoological standpoint, both the free-living and the parasitic species of 

 amoebae belong to many different genera. 



There can be little doubt that the two intestinal amoebae of man 

 commonly known as Entamoeba coli and E. histolytica are co-generic. 

 The characters supplied by their nuclear structure, their cysts, and their 

 development and morphology generally, warrant their inclusion in the 



• Leidy's paper was long overlooked, and his genus forgotten until attention was 

 called to it by Chatton (1910). It may be noted here that Leidy repeated his definition 

 of Endamoeba in his large work on the freshwater rhizopods (Leidy, 1879 a, footnote 

 p. 300), which also seems to have been generally overlooked. 



