THE FORMATION OF GERM-CELLS 21 7 



provided for in this case ; it is at any rate stated by Loeb * in a 

 recent paper that a shedding and new forniation of the crowns 

 occurs periodically. The same writer also showed by experi- 

 ment that, under favourable circumstances, crowns may bud out 

 at any point of the stem, either at the distal end or at the base. 

 On the other hand, he never succeeded in getting the root-like 

 organs of attachment to be produced at the apical end. 



No one will be surprised that such a growth did not occur who 

 agrees with me in looking upon all these processes of regenera- 

 tion and budding as resulting from adaptation. Under natural 

 conditions the apex of a stem could hardly be situated in such a 

 position as to render the formation of roots necessary, for it 

 never conies to lie upside down in the earth, and consequently 

 none of the cells in the apex contain ' rhizogenic idioplasm' 

 (' Wurzel-Idioplasma'). On the other hand, however, it is easy 

 to understand why the power of budding exists in such a marked 

 degree in polypes, if one considers how liable the soft body is to 

 be attacked by crabs, worms, gasteropods, Pycnogonids, and 

 other small enemies. If these polype-stocks did not possess the 

 power of continually producing new crowns, — i.e. new individuals, 

 — when the old ones have been bitten off, the whole colony 

 would soon perish owing to the absence of 'nutritive persons.' 

 The fact that regeneration is possible to such an enormous ex- 

 tent results, at any rate in part, from the aggregation of persons 

 to form the higher stage of individuality of the stock. For such 

 a combination of individuals procures the advantage of perma- 

 nent nutrition as long as all the individuals of the stock have not 

 fallen victims to their enemies, and thus it is favourable to the 

 production of new buds. 



Amongst the Poly 20a the case is very similar. In many of 

 these animals the normal form of gemmation takes place with 

 great regularity, and the region at which the next bud will arise 

 can be predicted beforehand : on this fact depends, as in the 

 case of the Hydroid polypes, the characteristic form of the 

 stock in the different species, which is sometimes branched like 

 a foliage tree, and sometimes like a fir-tree or a feather. In these 

 animals, therefore, definite cells must be provided with ' blasto- 

 genic' idioplasm in advance, and merely the stimulus due to ordi- 



* Jacques Loeb, ' Untersuchungen zur physiolog schen Morphologie der 

 Thiere,' I, Uber Hetermorphose,' Wiirzburg, 1891. 



