GEMMIPAROUS AND FISSIPAROUS REPRODUCTION. 157 



withers away, and the animal is thus detached and becomes 

 independent. Others remain through life united to the parent 

 stalk, and, in this respect, present a more striking analogy to 

 the buds of plants. But in the polyps, as in trees, budding 

 is only an accessory mode of reproduction, which pre- 

 supposes a trunk already existing, originally the product of 

 ovulation. 



330. Reproduction ly division, or fissiparous reproduction, 

 is still more extraordinary ; it takes place only in polyps and 

 some infusoria. A cleft or fissure at some part of the body 

 takes place, very slight at first, 

 but constantly increasing in 

 depth, so as to become a deep 

 furrow, like that observed in the 

 yolk, at the beginning of embry- 

 onic development ; at the same 

 time the contained organs are di- 

 vided and become double, and thus two individuals are formed 

 of one, so similar to each other that it is impossible to say which 

 is the parent and which the offspring. The division takes place 

 sometimes vertically, as, for example, in Vorticella, (Fig. 

 133,) and in some Polyps, (Fig. 134,) and sometimes trans- 



Fig. 133. 



Fig. 134. 



versely. In some Infusoria, the Paramecia, for instance, 

 this division occurs as often as three or four times in a day. 

 331. In consequence of this same faculty, many animals 

 are able to reproduce various parts of their bodies when 

 accidentally lost. It is well known that crabs and spiders, 

 on losing a limb, acquire a new one. ^The same happens 

 with the arms of the star-fishes. The tail of a lizard is also 



14 



