Dr. M. Verworn's Biological Studies of Pfotista. 167 



fragments takes place on a much larger scale than in Poly- 

 stomella. 



It may be a question what is the reason of the phenome- 

 non that two forms of Khizopods behave so differently with 

 regard to the regeneration of their shells as Diffltigia and 

 Polystomella or Orbitolites. There must evidently be a 

 priucipial diflference between the shells of the two forma 

 which accounts for this difference, and I do not think I am 

 far wrong in finding this in the mode of production of the 

 shells. In Dijjiugia^ as in all Monothalamia, the shell origi- 

 nates at the moment of fission, and is completely finished at 

 the separation of the new individual. No subsequent altera- 

 tions occur, and especially, as Gruber justly notes, no growth 

 of the shell takes place. The protoplasmic body has there- 

 fore ceased to have any secretory relations with the shell, the 

 faculty of shell-formation has ceased. In consequence 

 injuries may be inflicted on the shell, or it may be removed 

 altogether, without the occurrence of any regeneration. 



The conditions are different in the production of the Poly- 

 thalamian shells. It must now be regarded as proved by a 

 number of observations that the Polythalamia reproduce by a 

 kind of spore-formation, although this process has not yet 

 been directly observed. At any rate we know that the 

 young Polythalamia occur within the body of the parent as 

 unilocular Protista. If these develop into perfect Polytha- 

 lamia, they form upon the original cliamber a new one, to 

 which another tiqw one is soon added, and so forth. From 

 tliis it follows that the Polythalamia, so long as they form 

 new chambers, must have the faculty of shell-secretion. The 

 reason that existed in the case of Diffiugia for the cessation 

 of the shell-secretion no longer exists here, and, in fact, the 

 Polythalamia do regenerate their shells. A natural conse- 

 quence of this mode of formation of the shell in the Polytha- 

 lamia is the phenomenon that the forms with comparatively 

 limited chamber-formation, such as Polystomella^ possess the 

 faculty of regeneration in a much less degree than the forma 

 with an exceedingly strong chamber-formation, like Orbito- 

 lites. The faculty of regeneration in the Polythalamia is 

 therefore proportional to the faculty of forming new chambers, 

 and the latter again indicates the duration of development ; 

 consequently the power of regeneration certainly persists 

 throughout the whole period of development. Gruber cha- 

 racterizes the addition of new chambers only as a growth, and 

 says, on another occasion *, that in the Protozoa in general 



* " Dimorpha nutans, eine Mischform zwisclien Flagellateu und 

 Heliozoen," in Zeitscbr. f. wisa. Zool. Bd. xxxvi. 



