CONTRIBUTIONS TO THE CYTOLOGY OF THE BACTERIA. 485 



into a discussion of this matter, but I should like to call 

 atteution to the exliaustive — but almost completely ignored 

 — work of Billet (1890), and the remarkable researches of 

 Mencl (1905) in this connection. Here will be found an 

 immense collection of facts bearing upon the matter. 



It appears to me probable that — just as in the case of 

 tlieir nuclei — the majority of Bacteria may possess a wide 

 range of variation in their outward form at different stages in 

 their life-histories. The matter can be decided, however, by 

 further research only : but it offers a vast field for future 

 investigation — investigation which is not only of a most 

 fascinating natui'e, but of whicli the i-esults also will be of 

 the greatest biological interest. 



Do Enucleate Bacteria Exist? — I wish to say a few 

 words here about the Ijelief which is often hehl, that the 

 Bacteria are a group of organisms which possess no structure 

 homologous with the nucleus present in the cells of other 

 protists, animals or plants. 



From a survey of the work which has been done upon the 

 cytology of the Bacteria, I think it may be stated with 

 absolute certainty that not a single bacterial species 

 has been proved to be devoid of a nucleus. I do 

 not say that a nucleus has been proved to be present in every 

 bacterial species: but I do maintain that a nucleus has 

 been demonstrated in a large number of species 

 of Bacteria, The probability is, therefore, that all Bac- 

 teria ai'e nucleate cells. That enucleate Bacteria may exist, 

 is, of course, a possibility Avhich cainiot be denied; but at 

 present there is absolu tely not a vestige of evidence 

 in favour of such a view. 



I should like also to di-aw attention to a sort of state- 

 ment about Bacteria which may be very frequently encountered 

 in biological writings. The following cpiotation will serve as 

 an instance of the sort of thing I mean : " It may be pointed 

 out that it is in these low forms of life that we must look for 

 a key to the secret of the origin of the cell nucleus, as well 

 as for data to determine the morphological character of the 



