122 



en trouve d'autres qui ont une allure absolument désordonnée". 



And: „ Ie mouvement des flagella est comparable a celui 



d'un fouet Ie mouvement de l'eau resultant de Taction des 



flagella doit être, dans l'ensemble, perpendiculaire a l'axe des 

 choanocytes". 



In close relation to these interpretations of the motion of the 

 flagella (as Fig. 56 f^, bid) is the way in which the movement of 

 the water within the flagellated chambers was supposed to be. 

 In the theory of Bowerbank, Lendenfeld (and of Cotte) one 

 should imagine this movement to be regular and rapid, passing 

 from the prosopyles through the chamber to the apopyle. In 

 this way, however, it would not be clear how the sponge is 

 able to capture the food particles from the circulating water; 

 for the greatest deal of it would flow rapidly through the canal- 

 system without ever having been in contact with the cells 

 lining the canals! Cotte resolves this difficulty in the following 

 way : „II est certain que cette disposition morphologique" (of the 

 prosopyles) „a pour résultat la formation d'un remous ou d'un 

 tourbillon au point oil I'eau pénètre dans la corbeille vibratile. 

 Dans cette dernière les flagella, par leurs battements actifs, pro- 

 duisent un brassage énergique de l'eau et par conséquent des 

 particules en suspension dans celui-ci". And: „Il y a en ce point 

 contact plus inüme de l'eau et des aliments qu'elle ren- 

 ferme avec les choanocytes qui sont les organes de l'absorption". 

 But this seems to be based on reasoning, not on personal observation. 



Therefore it has been the great importance of the theory of 

 VosMAER and Pekelharing (62), that, based on experiments and 

 observations of the motion of flagella and the water-current itself, 

 it explained these phenomena in such a way, that it was evident 

 at once that such a movement of the water in the flagellated 

 chambers, as was stated by the investigators, was exceedingly 

 fit for bringing food particles within reach of the sponge-cells, 



I am now going to treat Vosmaer and Pekelharing's theory 

 more at large, as it has also been the starting-point of my own 

 research. Their principal experiment, giving most important obser- 

 vations, was made directly in the neighbourhood of the habitat 



