138 



ivaif hij a diagrammatic figure {Fi(j. 63). This figure does not 

 nood special explanation ; it is planned after Fig. 55, inentioned 

 above (p. 120). It sJwivs hoir the water must flow rcq)ldly and 

 rcrjuhtrly from the prosopyles (there is onhj one indicated here, 

 hut there are 2 — 5 in a chamber) between the cell-bodies and the 

 collars of the choanocytes to the base of the flagella {here really 

 the opening of the collars), to be pushed from, there by the fta- 

 gellar motions to the centre of the chamber, thence to floir airay 

 through the apopyle. It is impossible to prove here (eg. by adding 

 carmine) that the current of water has indeed entirely this 

 course, because — the next chapter will show this — the carmine 

 grains, carried along by the water between the choanocytes, are 

 kept there. This penomenon, however, proves already quite 

 siifficiently that the Avater-current within a chamber has in fact 

 the course given here (Cnf. Fig. 65, 66). 



If one asks about the differences of the water-pressure within 

 the canal-system of the sjwngCj it is quite clear that, with tlio 

 diagram given here (Fig. 63), this pressure must bc highest in 

 the centre o£ the flagellated chamber (higher than in the sur- 

 rounding water) and lowest (lower than in the surrounding water) 

 at the flagellar bases, while it is increased exactly in and by the 

 zone of the flagella. In order that a powerful, steady current 

 may be maintained by the chamber and that, therefore, the water 

 may enter rapidly and exclusively at the prosopyles and flow 

 out by the apopyle, the structure of the flagellated chamber must 

 comply with definite requirements. And these requirements do 

 not only count for the sponges of the type of Spongilla but mu- 

 tatis mutandis for sponges of any canal-system, either Calcaria or 

 Incalcaria (provided of course that there exists the same flagellar 

 motion). These requirements are: that the incurrent openings 

 (prosopyles, pori) of the chambers (mastichore) are relatively 

 narrow, the excurrent openings (apopyles, osculum) relatively 

 wide and that the former are placed among the choanocytes (all 

 this is generally realized). For the high pressure in the centre 

 of the chamber naturally makes the water flow out through the 

 largest opening, while over and above the flagellar motion in 



