30 Dr. F. von Wagner on 



former and accepting the latter of these hypotheses. We 

 justly regard the secretion of a cyst as a protective formation 

 secondarily acquired and owing its origin to the existence of 

 fission. 



The majority of Infusoria, such as Stentor for instance, 

 preserve their species by means of a form of fission in which 

 the formation of a new peristome and pharynx is to be 

 observed in one of the two animals in process of development. 

 Phenomena of this nature, which we shall meet with in the 

 fission of higher animals of all kinds, have long been included 

 under the term '' regeneration^ The question which we put 

 in the case of cystic fission leads to a similar answer when 

 applied to the mode of reproduction found in Stentor. The 

 regeneration of the organs which we have mentioned does not 

 imply something fundamentally new, but is a consequence 

 which necessarily results from the organization of the dividing 

 animal, the effect of which is to enable the posterior zooid to 

 maintain an independent existence. It is easy to see from 

 the context that in the case of the anterior fission-product, 

 which is from the first in possession of the original structures 

 and therefore of the conditions of an independent life, no, or, 

 to be more exact, scarcely any, regeneration is necessary. 



The examples which have been adduced show that certain 

 forms of fission in the Protozoa include accessory processes, 

 among which the phenomena of regeneration at least are seen 

 to be necessary^ and in many cases of fission must attain the 

 importance of a conditio sine qua non. In consequence of 

 this, however, that which in the case of the Amoeba is effected 

 by the fission, the actual process of division — originally a 

 form of reproduction in itself — becomes in the case of Stentor 

 a stage in the fission of this Infusorian, which is also charac- 

 terized by regeneration. The latter mode of reproduction, 

 therefore, when contrasted with that of Amoeba, signifies a 

 higher and more advanced form of fission, and may be desig- 

 nated as "paratomy^^ (i.e. ^^ secondary form of fission^'') ^ 

 as opposed to architomy. The process of division, which is 

 the essence of architomy, appears as a stage in paratomy as 

 " dissection " or " separation^ 



I now proceed to the consideration of another mode of 

 reproduction among tlie Protozoa, namely gemmation. The 

 multiplication of Podophrya may serve as an example. 



We are here confronted with a phenomenon which is not 

 to be understood from the ensemble of the points of view 

 which we have adopted for the consideration of fission, and is 

 therefore virtually new : this is a special kind of growth. 

 While in the case of Amoeba and Stentor the increase in size, 



