24 MANUAL OF ZOOLOGY. 



of another individual secured at intervals. Amongst the 

 higher animals sexual reproduction is the only process whereby 

 new individuals can be generated. 



II. Non-sexual Reproduction. Amongst the lower animals 

 fresh beings may be produced without the contact of an ovum 

 and a sperm atozoid ; that is to say, without any true generative 

 act. The processes by which this is effected vary in different 

 animals, and are all spoken of as forms of " asexual " or 

 " agamic " reproduction. As we shall see, ho\vever, the true 

 " individual " is very rarely produced otherwise than sexually, 

 and most forms of agamic reproduction are really modifica- 

 tions of growth. 



a. Gemmation and Fission. Gemmation, or budding, con- 

 sists in the production of a bud, or buds, generally from the 

 exterior, but sometimes from the interior, of the body of an 

 animal, which buds are developed into independent beings, 

 which may or may not remain permanently attached to the 

 parent organism. Fission differs from gemmation solely in 

 the fact that the new structures in the former case are pro- 

 duced by a division of the body of the original organism into 

 separate parts, which may remain in connection, or may under- 

 go detachment. 



The simplest form of gemmation, perhaps, is seen in the 

 power possessed by certain animals of reproducing parts of 

 their bodies which they may have lost. Thus, the Crustacea 

 possess the power of reproducing a lost limb, by means of a 

 bud which is gradually developed till it assumes the form and 

 takes the place of the missing member. In these cases, how- 

 ever, the process is not in any way generative, and the pro- 

 duct of gemmation can in no sense be spoken of as a distinct 

 being (or zooid). 



Another form of gemmation may be exemplified by what 

 takes place in the Foraminifera, one of the classes of the 

 Protozoa. The primitive form of a Foraminifer is simply a 

 little sphere of sarcode, which has the power of secreting from 

 its outer surface a calcareous envelope ; and this condition 

 may be permanently retained (as in Lagena). In other cases 

 a process of budding or gemmation takes place, and the prim- 

 itive mass of sarcode produces from itself, on one side, a 

 second mass exactly similar to the first, which does not detach 

 itself from its parent, but remains permanently connected with 

 it. This second mass repeats the process of gemmation as 

 before, and this goes on all the segments remaining attached 

 to one another until a body is produced, which consists of a 

 number of little spheres of sarcode in organic connection 



