THE PRINCIPLES OE CLASSIFICATION 73 



of this organism, until there is evidence that there are other 

 distinctive differences between the different classes of threads. 



(4) Cilia Insertion : Presence or Absence of Cilia. — An 

 investigation was instituted (Ellis (2 — 3)) on the mode of inser- 

 tion of the cilia to ascertain its constancy in the life-history 

 of a species. A culture of a species of Bacillus was kept 

 for several months, under different conditions. At frequent 

 intervals cilia preparations were made, and it was found 

 that under all conditions the peritrich ciliation was main- 

 tained. l"he same procedure was followed with a culture of 

 Pseiidomonas, with the same result, namely, that the polar 

 ciliation characteristic of this genus was also a constant feature. 

 So far as it was possible to conclude from the limited scope 

 of these experiments the mode of ciliation may be used for 

 purposes of classification. 



A distinction must also be made between organisms pro- 

 pelled by cilia, and others, like Beggiatoa alba, that are motile, 

 but which are apparently without cilia. Even if later re- 

 searches show that Beggiatoa and similar organisms do possess 

 cilia, these are almost certain to be of a different character from 

 the cilia of the bacterial organisms known at present to possess 

 them. Hence it may be possible with further knowledge 

 to make use of this fundamental difference in the mode of 

 ciliation. 



Migula in his classification made use of the number of cilia. 

 In the author's experience the number of cilia has been found 

 to vary in the same species. The cilia of Spirillum voliitans 

 were found to vary from one or two up to thirty and even a 

 greater number. The number of cilia seems to have some 

 relationship to the amount of slime formation, and this in its 

 turn depends on the nature of the external cultural conditions, 

 and the other factors which promote or retard growth. Hence 

 the mode of insertion of cilia may be used for classification, 

 but not tlieir number. 



(5) Pleomorphism. — In Chapter I. it has been shown that 

 some of the sulphur bacteria are pleomorphic; for example, 

 that the organism known as Lam.procystis is a form that occurs 

 in the life-history of at least three organisms, namely Bacterium 



