478 C. CLIFFORD DOBELL. 



I do not believe a single fact of any importance has been 

 found whicli speaks against my results. lu matters of inter- 

 pretation, of course there is considerable difference of opinion 

 already existing; but I am convinced that no interpretation, 

 other than that which I have given, can be found which will 

 fit all the facts known to us at present. How far such a con- 

 viction is justified further work alone can show. 



So far I have considered only the Bacteria themselves, and 

 I believe the evidence which I have given from this group 

 alone is suflScient to establish the fact that Bacteria are 

 nucleate cells. Considerable additional evidence may, how- 

 ever, be adduced from analogy with two other groups of 

 organisms — the Protozoa and the Cyanophycese. In the 

 Protozoa, a chromidial form of nucleus occurs in many 

 different organisms, as a transient stage in the life-cycle. It 

 may also occur as the normal vegetative condition. It is un- 

 necessary to enter into this subject in detail here. The reader 

 will find a condensed account of chromidia in a paper which 

 I have previously published (see Dobell, 1909b). A nucleus 

 in the form of irregular strands, networks, granules, etc., 

 scattered through the cytoplasm, also occurs in Protozoa — 

 especially in the Infusoria (cf. Dobell, 1909a). 



In the Cyanophycea?, analogous nuclear conditions probably 

 obtain. It is impossible in the present paper to enter into 

 a discussion of the vexed question of the nucleus in this group, 

 but I should like to call attention to two recent contributions 

 to the subject Avhich have been made as a result of careful 

 cytological work. I refer to the work of Gardner (1906) and 

 Guilliermond (1907a) Gardner describes and figures nuclei 

 in the form of networks, granules, and irregularly branched 

 filaments. Guilliermond describes similar structures, and also 

 nuclei in Nostoc which resemble those of Micrococci, and 

 nuclear filaments, like those of Bacillus spirogyra, in 

 Ilivularia. If analogies were wanting for the structures 

 which I believe to be nuclei in Bacteria, they could be found 

 therefore without any great diflficulty in the nuclei of other 

 organisms. 



