542 



GENERAL PHYSIOLOGY 



pieces regenerates the parts lacking in it. The wounds close, 

 and the lower part of the cell at once arranges its substance so 

 that a new peristome appears with the characteristic spiral of 

 cilia and a mouth-opening, while the upper part becomes extended 

 so that a new foot-piece is developed, with which the new Stentor 

 attaches itself. Thus, in a short time by the deposition of particles 



II 



FIG. 265. Silicious spicules of sponges. /, Scheme of the production of a quadriradiate spicule 

 between four vascular spaces. (After F. E. Schulze.) //, Various forms of silicious spicules. 



from the interior of the body at the place of the wound, a complete 

 Stentor is developed from each piece (Fig. 264). This fact of re- 

 generation is now very easily understood. Since in the process of 

 differentiating organised cell-forms every particle attracts and 

 holds fast other specific particles and upon the withdrawal of the 

 latter in metabolism, at once attracts and holds corresponding 

 particles again, so in regeneration the particles existing at the 

 wound, which are separated from their neighbours by the cut, 



FIG. 2(56. Scheme of the production of various skeletal forms by the excretion of skeletal sub- 

 stance into the walls of a vacuolar system. (After Dreyer.) 



must immediately attract and attach to themselves corresponding 

 particles, if they are obtainable. Since, however, in such a 

 division of the body metabolism experiences no fatal disturbance, 

 the necessary particles are still, as formerly, brought in by the 

 stream of matter, and can attach themselves to the others as the 

 peculiar quality of each one demands. But if the metabolism has 



