REPRODUCTION 



the length-cleavage, and the two are at length made 

 to coincide, twofold division is changed into fourfold 

 division. And when the process is repeated in quick 

 succession, and the body falls at last into a number of 

 small and equal pieces, we have manifold division (polyt- 

 omy); as in the spore - formation of the sporozoa and 

 rhizopoda, and in the embryonic sac of the phanerogams. 



Asexual propagation by budding is chiefly distin- 

 guished from segmentation by the fact that the deter- 

 mining transgressive growth is only partial in the one 

 and total in the other. The bud produced is, therefore, 

 younger and smaller than the parent from which it 

 issues ; the latter may replace the lost part by regenera- 

 tion and produce a number of buds simultaneously or 

 successively without losing its individuality (whereas 

 this is destroyed in division). Propagation by budding 

 is rare among the protists, and more common among 

 the histona — that is, with most of the tissue-plants and 

 the lower, stock-forming, tissue-animals (ccelenteria and 

 vermalia). Most stocks (cormi) are formed by a sprout 

 or person shooting out buds which remain united to it. 

 The layer and shoots of tissue-plants are detached buds. 

 The two chief kinds of gemmation are terminal and 

 lateral. Terminal budding takes place at the end of 

 the long axis, and is not far removed from transverse 

 division (for instance, the strobilation of the acraspedae 

 medusas and the chain tape-worms). Lateral budding 

 is much more common; it determines the branching of 

 trees and generally of complex plants, and also of the 

 tree-shaped stocks of sponges, cnidaria (polyps, corals), 

 bryozoa, etc. 



A third form of asexual reproduction is the formation 

 of spores or "germ-cells," which are usually produced 

 in great numbers inside the organism, then detached 

 from it, and developed into new organisms without 

 needing fertilization. The spores are sometimes motion- 



243 



