MULTIPLICATION BY FISSION 1 45 



CHAPTER III 

 MULTIPLICATION BY FISSION 

 I. Preliminary Remarks 



Until a short time ago the process of multipHcation by gem- 

 mation was looked upon as having been derived phyletically from 

 the corresponding process by fission, and the two were thought 

 to be closely related, and connected by gradual transitions. Von 

 Wagner * has, however, recently attempted to contest this 

 opinion, and to show that the two processes should be more dis- 

 tinctly separated from one another than they have hitherto been, 

 and that they are, in fact, genetically distinct. By the term 

 (fission), Wagner means to indicate a process of multiplication 

 which is preceded by a symmetrical growth of the parent 

 organism, by means of which the individuality of the latter be- 

 comes changed and to a certain extent abolished : the term 

 (gemmation), on the other hand, he takes to mean a process of 

 multiplication w-hich is preceded by an unsymmetrical (differ- 

 ential) growth of the parent organism, in which the individuality 

 of the latter is not abolished and its place taken by a new 

 individual. 



This view I agree with in so far as I am convinced that in 

 multicellular organisms the processes of multiplication by fission 

 and budding have not arisen genetically from one another : these 

 processes diifer so essentially that it will be advisable to discuss 

 them separately. 



Following von Wagner's example, I shall include under this 

 head of fission all the processes of asexual multiplication which 

 occur in the flat-worms {Tiirbella^'ia^ Cestoda), the annelids 

 proper {SyllidcB, NaidcB, TubificidcE^ &c.), and also in the higher 

 Medusae (strobilation) . In all these cases multiplication is 

 effected by the division of the parent animal into two or more 



* Franz von Wagner, 'Zur Kentniss der ungeschlechtlichen Fortpflanzung 

 uon Microstoma nebst allegemeinen Bemerkungen iiber Thielung u. 

 Knospung im Thierreich,' Zool. Jahrbiicher, Abth. f, Anat, u. Ontogenie, 

 Bd. iv., Jena, 1890. 



