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out. Such a period of weak motion may be repeated several times. 

 As is shown in the figures, the collars were sometimes visible 

 for a small part; generally they appeared more clearly when the 

 motion had almost ceased (sign of relaxation of the protoplasm- 

 contractility when death is approaching?). 



We might now go into a theory about the contractions of the 

 protoplasm, which must take place in a flagellum in order to 

 bring about these (spiral-)waves. And we should be the more 

 justified in doing so, 1st because the spiral- or undulating-motion, 

 as we shall see presently, is in fact the normal way of flagellar 

 movement of the choanocytes, and 2nd because in my opinion it 

 is very likely that in the changing of this movement by exhaustion 

 we could find a good starting-point for such a theory about its 

 mechanism. 



As all this, however, would only be more distantly connected 

 with the subject we are treating at present, I prefer to leave it 

 till lateron. 



Though we may have shown now, that the normal motion 

 of the flagellum is more likely a spiral- or waving- than a 

 rowing-motion, as the former investigators had found, we have 

 not yet proved, however, that the tiortnal motion of the flagella 

 within the intact flagellated chambers is really also a spiral- or 

 undulating one. For up to now I described observations of ravelled 

 sponge tissue. 



Here my method^ which makes it possible to observe wholly intact 

 normally living sponge tissue with oil-immersion for a long time, 

 has rendered me good service. This method has been described on 

 p. 12 — 13. Only Spongilla is fit for it (as Ephydatia grows too 

 slowly) and exclusively in summer. If the microscopic preparations 

 have been made with care and if the outward circumstances have 

 been favourable (sufficient warmth !), then we find, within a week's 

 time, the vigorously acting flagellated chambers with in- and ex- 

 current canals everywhere in the sponge-rim — so in the newly 

 formed tissue. 



9 



