158 SOME MINUTE ANIMAL PARASITES 



appear towards the end of the life of the entamceba, 

 and are now known to be buds produced by an 

 exhausted trophozoite. 



As before mentioned, small trophozoites producing 

 small cysts have been described by Elmassian under 

 the name of E. minuta. This organism multiplies 

 by schizonts which form four daughter merozoites. 

 They also pass from host to host as small cysts that 

 give rise to four spores. Thus, apart from its 

 smaller size, E. minuta is like E. tetragena. 



E. histolytica, E. tetragena, and E. minuta how do 

 they form one complete life-cycle and not three life- 

 cycles ? The first step in the matter was taken by 

 Fantham (April, 1911), who pointed out the need 

 for the consideration of the great polymorphism 

 shown by Entamoebse, and stated that " probably 

 E. minuta is merely a variety of E. tetragena." 

 Subsequent work has proved the truth of this sugges- 

 tion. Darling more particularly has worked on the 

 subject, and by experiments with kittens has shown 

 that by successive passages from host to host it is 

 possible to produce any known form corresponding 

 to E. histolytica, E. tetragena, or E. minuta. Com- 

 mencing with the large trophozoites with a nucleus 

 poor in chromatin, once said to be characteristic of 

 E. histolytica, he showed by experiments that the 

 character of the nucleus gradually changed until it 

 showed the large quantity of chromatin and promi- 

 nent karyosome identified with E. tetragena. The 

 different sizes in the cysts and the production of 

 small generations was shown to depend on the near- 

 ness or remoteness of the encystment period to that 



