157 



„dass die Kragenzellen wirklich die einzigen direct nahrungs- 

 aufnehmende Elemente sind". 



While on the other hand Minchin (45) wrote rightly: „There 

 can be no doubt whatever, .... that in many sponges at least 

 the collar cells are very active in capturing food. On the other 

 hand, these cells are from their nature and size incapable of in- 

 gesting large bodies such as Infusoria or Diatoms. Food of the 

 latter kind could only be absorbed by becoming entangled in the 

 webs of tissue in the incurrent canal system, there to be absorbed 

 by phagocytic wandering cells, or, it may be, by porocytes". 

 Especially this last supposition, the ingestion by porocytes (here = 

 plasmic layer, p. 154), has proved to be exact. 



D. THE DIGESTION OF FOOD IN THE FRESH-WATER 

 SPONGES. 



I shall be quite short about this subject, as I only possess 

 very few other data concerning it, except all I told above in 

 extenso about the digestion of the green symbiotic algae in the 

 sponge tissue, under the head „Chlorophyll" (p. 16 — 17, 42 — 45, 

 94—116). 



As we have seen, however, (p. 96) that exactly the symbiotic 

 algae are a very important, perhaps even the chief source of 

 nourishment for the fresh-water sponges, we certainly may con- 

 sider the results, regarding their digestion, to be decisive with 

 regard to the problem of the digestion in the fresh- water sponges 

 in general. 



We saw that the symbiotic algae, which the sponge has cap- 

 tured from the water in the ways described in the preceding 

 chapter and carried on to the amoebocytes, die within those 

 amoebocytes, either for a part, or all of them, and are digested 

 there and dissolved, while the decomposition-products come to the 

 benefit of the sponge (p. Ill — 113). This digesting and dissol- 

 ving mostly took place free in the protoplasm of the lodging 

 cells, sometimes however within a vacuole (p. 97). As I remarked 



