26 Dr. F. von Wagner oir 



means makes a strict distinction between fission and gemma- 

 tion (cf. note a, below). 



The above historical sketch, all incomplete though it is, 

 renders sufficient evidence of the uncertainty which blocks 

 the way of an absolute criticism of the reproduction of Micro- 

 stoma ; so that in spite of the material progress which has 

 been effected in our knowledge of the process since the inves- 

 tigations of Schmidt, the theoretical interpretation of the 

 subject (like that of many similar processes in other animals, 

 especially worms) appears to have been in no way advanced. 



This surprising state of things is due not so much to the 

 peculiar phenomena presented by the asexual reproduction of 

 Microstoma, as to the general fact that uncertainty has arisen 

 as to what is to be regarded as fission and what as gemma- 

 tion. This uncertainty, it is true, appeared latterly to have 

 been abolished by the view, which met with constantly 

 widening acceptance, that fission and gemmation are processes 

 which are most intimately related to one another. As a 

 result of this the question whether in a particular case this or 

 that interpretation was correct naturally lost its importance 

 (note a). 



Nevertheless the view which maintains that fission and 

 gemmation are fundamentally only two different representa- 

 tions of one and tlie same form of reproduction does little 

 more than clothe the old uncertainty in a new garb ; for if 

 we would discover relations of whatsoever kind between 

 fission and gemmation we must first have come to an under- 

 standing as to the essential characteristics of the two repro- 

 ductive methods. Yet every one who is acquainted with the 

 subject is aware how little this condition is fulfilled at the 

 present time. The manuals are lackingin precise statements*; 

 in particular cases we help ourselves by distinguishing, e. g. 

 in the Syllidse and their allies, a " fissiparous " from a 

 " gemmiparous " reproduction, or by paraphrasing so-called 



a. Thus the question whether the strobilation of the Medusae is to be 

 regarded as simple transverse fission or as terminal gemmation appears 

 to Claus " to be in itself a case of splitting hairs." — C. Claus, ' Unter- 

 suchungen iiber die Organisation und Entwicklung der Medusen,' Leipzig, 

 1883, p. 17. 



* The present paper was practically completed when I came across 

 Heft 2 of HatscheK's ' Zoologie.' The observations of this author upon 

 fission and gemmation contain a wealth of appropriate standpoints for the 

 consideration of the question, and I hasten to refer the reader to them, at 

 any rate for the sake of comparison, since a detailed discussion of his 

 remarks would here lead us much too far afield, consideriug the difier- 

 ence in our fundamental ideas of the processes {cf. Hatschek, ' Lehrbuch 

 der Zoologie,' Heft 2, Jena, 1889, pp. 216 d sqq.). 



