218 THE PROTOZOA 



first stages in the development of sexual reproduction. 1 It is certainly 

 reasonable to argue that the mutual attraction of two previously 

 separated blastomeres of the frog's egg (Roux, '94), or the reunion 

 of an? amputated pseudopodium with the main body of Difflugia 

 (Verworn, '88; Rhumbler, '98), the union of numerous naked Amoeba 

 verrucosa into a common aggregate (Rhumbler, '98), and the union 

 of two conjugating individuals, are all phenomena of the same order. 

 The phenomenon in Amoeba appears to have no bearing upon the 

 function of reproduction, for, according to Holman's and Kiihne's 

 accounts, conjugation is not followed by reproduction, while true 

 conjugation phases may yet be found in other stages of the life- 

 history of Amoeba (Fig. 118, D). The discovery by Schaudinn of 

 swarm-spores in the allied form Paramceba, and of the union of 

 swarm-spores in the more or less closely allied rhizopod Hyalopus, 

 makes it not at all improbable that the same 

 thing may occur in Amceba verrucosa. 



Thus cytotropy, leading first to contiguity, 

 may result in plastogamy, or the fusion of cell- 

 plasms. The protoplasm, however, must be 

 in the proper plastic condition for such a 

 union. Some forms, such as the Mycetozoa 

 and some Heliozoa, are apparently always in 

 this condition, and contact results in fusion. 

 In many such cases plastogamy leads to noth- 

 Pig. 119. -^Conjugation in in g further, nuclear fusion (karyogamy) not 

 vuigaris Ehr. occurring. Many instances of such union are 

 found amon g the Sarcodina, and up to the 

 present time they have been seen nowhere 

 else. These unions take place not only in viscous forms such as the 

 plasmodia of Mycetozoa, Actinophrys or Actinosphcerium, but also 

 in the denser types of Rhizopoda. Thus, in Arcella, two or more 

 individuals may fuse together (Fig. 119), and in the shelled rhizopod 

 Difflugia lobostoma, Rhumbler ('98) has shown that two, three, or 

 four individuals may be found in plastogamic union in from six to 

 ten per cent of all cases. He also made the interesting and signifi- 

 cant observation that this union cannot be induced at will, and 

 concluded that plastogamy takes place here only under certain 

 conditions of the plasm. 2 



Such plastogamic union in the cases cited has apparently no effect 

 upon the united organisms; both Johnson and Schaudinn found no 

 changes in the nuclei in Actinophrys and Actinosphcerium, and 



1 Cf. Cuenot ('97) ; Rhumbler ('98). 



2 Cf. union during the amoeboid stage of Cercomonas and other flagellates. 



