THE STRUCTURE OF BACTERIA. 2? 



of the perpetuation of the species under the 

 guise of a resting-stage or spore. Cohn was the 

 first to observe that sometimes the single cells 

 that become detached from a filamentous bac- 

 terium or that are set free by the breaking up 

 of the filament, do not possess the character of 

 ordinary vegetative cells but rather resemble 

 the gonidia, conidia or spores such as are found 

 in some algae or moulds, and Hueppe and De 

 Bary subsequently showed that in many bac- 

 terial species single members of a chain may 

 acquire the resistant properties and the func- 

 tion of the resting-stage. For distinction these 

 were called arthrospores (Figs. 3, 13, 19). It 

 appeared in some instances as if almost any 

 individual cell, while not unlike the others in 

 form, might under certain conditions become an 

 arthrospore. Hueppe observed that such a cell 

 would sometimes be insulated or protected 

 against harmful influences by a mantle of the 

 adjacent dead cells formed about it. In other 

 cases the arthrospores increase in size and ac- 

 quire a compact membrane, as happens also 

 in some algae. In some leptothrix-forms the 

 gonidia are found in thickenings of the sheath 

 which must therefore be considered as the 

 spore-bearer or sporangium. 



True arthrospores are spheroidal in form, but 

 this fact must not lead us to confound them 



