160 



quantité de ceux-ci. Les cellules sphéruleuses entrainent dans 

 leur élémination quelques-unes des particules qui ont été déver- 

 sées dans la substance fondamentale. La plus grande quantité de 

 celles-ci, après avoir été transportée dans tout l'organisme par 

 les amibocytes, est directement expulsée par la substance inter- 

 stitielle ; quelques-unes sont transportées jusqu'aux canaux par 

 les amibocytes qui les y rejettent". As far, however, as I can 

 gather from the description, Cotte has never observed the often 

 mentioned ejection of particles by the „substance interstitielle" ; 

 but he did observe the ejection of (or by) „cellules sphéruleuses" 

 into the canals, as well as defecation by choanocytes (within the 

 collar, just as in the Choanoflagellata !). Cotte experimented on 

 Reniera simulans and Sycandra raphanus. 



As one sees, the whole problem of excretion and defecation is 

 still a long way from being solved ; particularly because so 

 often hypothesis and observation have been intermingled. 



Noiv, jj» mijself have come to the conclusion, hy ohserving the 

 phenomena in my normally living microscopic lu^eparations of 

 sponge tissue^ that defecation — and very likely excretion at the 

 same time — takes place on a large scale hy means of vacuoles, 

 which occur along the tvalls of the (excurrent) canals in an ap- 

 parently undifferentiated plasmic substance^ that in reality con- 

 sists of amoeboid cells. 



I now pass on to my experiments. 



A proof, that defecation — so a process, by which solid par- 

 ticles captured from the water and food-rests, which are of no 

 use to the sponge, are removed from its tissues — is really 

 acting in the sponge-body, follows already from what I said in 

 the first part of this paper (p. 15 — 16). There we saw that a 

 sponge, newly caught from nature, has a dirty (green or brown) 

 colour, as its tissue is loadon with particles from the (also brownish) 

 water of the lake; this dirty tint, however, entirely disappears 

 and the bright (green or creamy white) colour comes in its place, 

 when the sponges have been cultivated for some days in pure 



