42 AMEBOID MOVEMENT 



vespertilio cannot be distinguished from those of verrucosa, radi- 

 osa, poly podia, Umax and guttula. Schepotieff ('10) in a similar 

 vein, writes : "Wir werden demnach so bekannte und so lange Zeit 

 als selbststandige und typische Amobenarten aufgefasste Formen 

 wie A. Umax, A. poly podia, und A. radiosa nur als Umwand- 

 lungsstadien andrer Arten bezeichnen diirfen." Glaser ('12) re- 

 marks : "The most reliable criterion for the classification of the 

 amebas is the division of the nucleus." Calkins ('12) takes the 

 same view on this point and states that in his opinion the ecto- 

 plasmic and endoplasmic characters of amebas conform to four 

 "types," viz., proteus, verrucosa, vespertilio and Umax. The 

 enormous amount of work that has been done on the nuclear di- 

 vision changes as compared with the small amount of work on 

 the cytoplasmic structure has thus naturally tended to an over- 

 estimation of the significance of the nuclear changes. 



There are objections to making the nuclear changes the basis 

 of the classification of the amebas. 



i. In the first place, to classify the amebas means not only 

 labeling the different species accurately, but also to assign to 

 them their proper place in the system of organisms. All organ- 

 isms are classified with this purpose in view. This is what is 

 meant by a natural system of classification as contrasted with an 

 artificial system based on only a part, arbitrarily selected, of each 

 of the organisms concerned. In the past all artificial systems 

 have been discarded. It is perhaps unnecessary to say that a 

 classification based on nuclear characters would be a highly arti- 

 ficial system. For in no group of organisms has it been found 

 possible thus far to use the nuclear changes as a basis of classifi- 

 cation. The great amount of labor that has been expended by 

 cytologists within recent years on the behavior of chromosomes, 

 and the immense amount of work done by the students of genetics, 

 has failed to show any specific relation whatever between the 

 external characters of organisms and the nuclear behavior. 3 In 



3 That is, resemblances in nuclear division stages are not correlated with 

 corresponding degrees of resemblance in somatic characters. It is not 

 generally held that the shape or size or number of chromosomes is cor- 

 related with any external characters. It is the presence of hypothetical 

 factors or genes which are held to be correlated with somatic characters 

 and their number or arrangement in a chromosome is not in any way 

 related to their character. 



