CHAP. XXXVI.] 



GENERATION. 



Fig. 252. 



525 



Vorticella Microstoma multiplying by spantaneous longitudinal division, from Ehreriberg. 



The joints of the common tape-worm multiply in this manner, 

 and after a time, when perfectly developed, become free and 

 separate from the trunk of the worm. Amongst the worms 

 (Annelida) reproduction takes place partly in this manner. In the 

 Nais, three or four young worms, resulting from the division of 

 the parent, may often be seen still connected with its body. As 

 these become developed, they are disconnected from the parent, 

 and, in their turn, give rise to others by a similar process. 



Fig. 253. 



NaTs proboscidea, multiplying by spontaneous transverse division, shewing the body of the parent 

 worm and three young ones in different stages of development, a. Point at which new segments are 

 being formed, after Miiller. 



In the above instances, multiplication by division occurs as a 

 natural process ; but there are many instances in which the parts 

 resulting from artificial division ultimately become developed into 

 a perfect animal. Thus a planaria, or a polyp, may be divided into 

 many segments ; and each portion has the power of absorbing to 

 itself nutriment, and of becoming developed into a perfect form. 

 The slightest handling, again, causes some animals to break up in 

 pieces, and each separate part becomes a new being. 



Multiplication by Gemmation. A bud consists of a mass of cells, 



