VEGETATIVE PROPAGATION 325 



nearly related the stock would degenerate and ultimately die out 

 altogether. In this particular instance each of the two Animal- 

 cules which have conjugated divides into two, and each half at 

 once divides again, so that multiplication is fourfold. By suc- 

 cessive divisions of the fertilized nucleus eight fragments are 

 produced, which become the macronuclei and micronuclei of the 

 four new individuals. There are other fragments which come to 

 nothing. The stages in conjugation and subsequent fission will 

 best be followed by reference to figs. 847 and 848. 



In a Bell-Animalcule {Vorticella) conjugation, instead of being 

 temporajy, as in the form just described, where two individuals 

 exchange nuclear fragments and then sepa- 

 rate, \% permanent; i.e. two individuals com- 

 pletely fuse together to give a compound 

 cell, which afterwards undergoes active fis- 

 sion. And the process differs in another 

 important respect, for the individuals which 

 fuse are of different size and nature. One 

 is a large fixed bell, the other a small free- rig, 849.-Permanent conjugation 

 swimming individual (fig. 849), the latter ti^LtrZT^lZ.T"'^''^' ^''' 



being a product of multiple fission (see . and b ar= successive stages in , he 



p. ^21). Both conjup-ation and subsequent fusion of a large fixed beii (i) and a 



i- ^ I -J <J 1 small free-swimming one (2). 



division are attended by complicated nuclear 



changes differing only in detail from those already described for 



the Slipper-Animalcule. 



Vegetative Propagation in Many-celled Animals (Meta- 

 zoa). — Some of the lower many-celled animals (Metazoa) regularly 

 propagate by fission or budding, and are also able to regenerate 

 lost parts with ease. The latter phenomenon is also exemplified 

 by animals higher in the scale, and even the most specialized 

 backboned forms are able to repair injuries to some extent. 



Vegetative Propagation and Regeneration in Sponges iPori- 

 fera). — A simple Sponge is commonly in the form of a cup or 

 vase, the walls of which are perforated by numerous small holes. 

 Sea-water streams through these into the central cavity, and 

 thence to the exterior through the larger opening {oscuhcm) at 

 the end of the body. Most Sponges, however, are far more 

 complicated than this, and take all sorts of shapes. Some are 

 compact masses, others flat incrustations attached to stones, &c. ; 

 others, again, branch like plants. Such forms as these are usually 



