1068 



As to the cause of the water-current the investigation and the theory 

 of VosMAER and Pekelharing ^) are now almost generally acknowledged 

 to be decisive. According to these, the motion of the flagella of the 

 choanocytes is irregular, going to and fro (as fig. Id), for which reason 

 the water-current in the flagellated chambers is not a regular stream, 

 but a whirling movement. In consequence of tliis motion of the 

 flagella the water-pressure on the inside of the wall of the flagellated 

 chambers is constantly changing, at one time it is higher than 

 outside the chamber, at another time lower. With a rise of pressure 

 the outflow of water through the prosopyles is checked by the 

 choanocytes acting as valves; if on the other hand the pressure is 

 lowered, the water will easily enter the flagellated chambers by 

 these openings between the choanocytes. The sponge must therefore 

 suck up water t)y its incurrent canals, and this flows out again 

 by the osculum. 



1 have myself now been able to establish, not only with my 

 normally living microscopic j)reparations and therefore with choanocytes 

 in wholly intact flagellated chambers, but also with isolated choanocytes 

 in ravel preparations of living tissue: l^^ That the above described 

 flagellar movement is not the normal one, but an abnormal 

 caused by exhaustion. 2"^^ That the normal movement takes place 

 in spiral- or wave-line, just as occurs in the Flagellates, in 

 the Choanoflagellates for instance; which movement consists in a 

 very rapid succession of waves of small amplitude, passing along 

 the flagellum from the base to the apex; by this means a current 

 of water is generated straight througli the aads of the flagellar spiral 

 and similarly in the direction from base to apex, whilst the water 

 comes to the base laterally (fig. \a, 2). By exhaustion wholly 

 different flagellar movements arise, with abnormal current of water, 

 which are best illustrated by some drawings (fig. Id^ — e) made directly 

 from the living object. The figure shows the successive stages of 

 movement of the flagellum of an isolated choanocyte, from immediately 

 after the isolation [la) till it came to rest 20 minutes later {\e). Tt 

 may be clearly seen how the movement of the flagellum and the 

 water-current, which immediately after isolation {\a) were still normal, 

 have already much degenerated 5 minutes later (Ic) ; and that after 15 

 minutes they take the form which was observed by Vosmakr and 

 Pekelharing: a relatively slow and irregular beating to and fro of 

 the flagellum loithont waves, whilst the water is moved to and fro 



1) Proc. Kon. Acad. v. Wetensch. Amsterdam, 26 Maart 1898. 



Verhandelingen Kon. Acad. v. Wetensch. Amsterdam, 2e Sect., VI, 3, 1898. 

 Arch. f. Anat. u. Physiol., Physiol. Abth., 1898. 



