THE LOBOSA 75 



In Pelomyxa (Bott [2]) amoeboid isogametes are discharged 

 from the body with a nucleus formed in a manner that suggests 

 that the number of the chromosomes is reduced (infra, p. 76). 

 These gametes conjugate to form a zygote (Fig. 10), which may 

 subsequently encyst. 



In Trichosphaerium (Schaudinn [26]) a large number of 

 biflagellate isogametes escape from the cyst and by exogamous 

 conjugation form zygotes which become amoeboid in character. 



Biflagellate isospores arise from the cystic stage of Paramoeba 

 eilhardi, but there is no evidence, at present, to show that they 

 conjugate. 



In Centropyxis (Schaudinn [27]) heterogametes are formed 

 which have a shell. After conjugation the zygote escapes from 

 the shell and forms a new one like that of the adult individual. 



Life-History. The recent rapid advance in our knowledge of 

 the life-history of Lobosa, due in large measure to the researches 

 of Schaudinn and R. Hertwig, suggests that in all cases the 

 developmental cycle that is passed through is both complicated and 

 varied. 



In order to illustrate the general character of these life- 

 histories, four examples may be taken for description. 



Endamoeba coli is found in the upper part of the human large 

 intestine, but unlike Endamoeba histolytica it does not appear to be 

 the cause of or associated with any particular form of disease. It 

 undoubtedly occurs in perfectly normal and healthy hosts. 



During the ordinary vegetative life in the intestine it multiplies 

 by simple fission with amitotic division of the nucleus. Occasionally 

 schizogony occurs, when the nucleus divides into eight by successive 

 mitoses and each of these nuclei becomes the nucleus of a daughter 

 amoebula. After a certain period of vegetative life, the normal 

 duration of which has not been estimated, the uninucleated amoebae 

 become encysted, and in that condition are passed into the lower 

 part of the large intestine, and so to the exterior with the faeces. 

 The complicated divisions and the conjugation of the nuclei during 

 and antecedent to complete encystment have already been described. 

 Many of the cysts undoubtedly perish, but the cysts with eight 

 nuclei when swallowed by another host will give rise to eight 

 amoebulae which infest the intestine of the new host. The cysts 

 with more than eight nuclei that are sometimes found in the faeces 

 are, according to Schaudinn, degenerating cysts, and never give rise 

 to active amoebulae. 



In Trichosphaerium, a marine rhizopod with peculiar radiate 

 pseudopodia and many nuclei, there are two phases in the life-cycle. 

 In the first phase the gelatinous investment is armed with radiating 

 apicules. It reproduces itself in this phase by simple binary or by 

 multiple fission, the pseudopodia being previously Avithdrawn. In 



