100 Regulation of Size in Unicellular Organisms 



of the species for which it has been described being 

 listed in table 9. In most of the instances included in 

 this table the fusion was actually watched. In some 

 the fusion was so complete that a single nucleus was 

 formed, with double or more the number of chromo- 

 somes; and the body was of the normal shape but of 

 enlarged size. Actual measurements of the dimensions 

 were made in only one or two of the studies referred 

 to; these are discussed elsewhere. The enlarged size 

 was said to be sometimes maintained for several gen- 

 erations, but apparently tendencies existed toward the 

 formation of individuals endowed with normal nuclear 

 and cytoplasmic quantities. Belar ('21) noted that 

 fused individuals tended to die, especially when more 

 than two nuclei were present ; so that there are distinct 

 disadvantages in the multiple condition, and natural 

 preventatives to continued propagation of such forms. 



Grafting. The artificial grafting of two cut indi- 

 viduals to one another was first performed by Cien- 

 kowski ('65) in the heliozoan Actinosphserium. In 

 one case he fused together five individuals, holding 

 them in contact by paper strips; soon afterwards the 

 giant individual underwent fission. This was possibly 

 in response to the large bulk of its substance. Judg- 

 ing from the frequency with which Actinosphseria fuse 

 spontaneously, it is questionable just how much the 

 manipulation had to do with the success of Cienkow- 

 ski's grafts. Prowazek ('01) got three Myxamebae to 

 fuse after cutting, but the fate of the resulting giant 

 was not described. Other attempts to induce fusion 

 by cutting have been conspicuously negative in re- 

 sult, as in the early investigation of Verworn ('91) on 

 the marine Thalassicola. 



In Ameba the possibility of inducing fusion has been 

 investigated several times. Approximation and cut- 

 ting have so far yielded no continuity of cytoplasms, 



