98 ELEMENTS OF BIOLOGY. 



hermaphrodite plants, where self-fecundation may, and cer- 

 tainly does, occur, provisions seem to exist by which per- 

 petual self-fertilisation is prevented, and the influence 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 Reprodiidion. — Amongst the lower animals 

 fresh beings may be produced without the contact of an 

 ovum and a spermatozoid ; 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, 

 however, the true " individual " is very rarely produced other 

 wise than sexually, and most forms of agamic reproduction 

 are really modifications of growth. 



a. Gem??iatio?i and Fission. — Gemmation, or budding, 

 consists 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 produced by a division of the body of the original 

 organism into separate parts, which may remain in connec- 

 tion, or may undergo 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 Crus- 

 tacea 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, however, the process is not in any way genera- 

 tive, and the product 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 



