Excretory Processes in Porifera. 493 



tliese particles, lie seems convinced tluit both in this form ami 

 in Tticliontlla labi/rint/iica tlie " spongozoa " are the actively 

 in>^esting layers. 



Sollas (1.")) has also verifieil these observations upon 

 colonies of Spoiujilhi, stating that the choanocytes alone take 

 up the particles of carmine. 



Ileider (7) experimented upon species of Oscarella^ and ho 

 seems to have been led to the same result. 



Von Lendenfeld (D) conducted a series of feeding experi- 

 ments upon the Aplysinitla^ and his results led him to believe 

 that the ingestion was conducted by the amoeboid niesoderm- 

 cells lining the subdcrmal cavities, and that the particles after 

 digestion by these cells were ejected into tiie flagellated 

 ehandK-rs and driven out by the choanocytes. He finds that 

 the choanocytes do absorb carmine particles, but believes that 

 these are soon ejected unchanged. 



It is quite |)Ossible that concurrently with the development 

 of subdermal cavities there is a change in the distribution of 

 the digestive function ; but it is difficult to believe that the 

 choanocytes should perform the function of ingestion (apart 

 from that of digestion) in so many simple sponges, and 

 that they should not only lose this function in Aplysinidae, 

 but should actually take on tlie special one of assisting 

 excretion. 



Jt is worth noting that the metabolic circuit which 1 make 

 out to be normal in Grantia is, allowing for the absence of 

 subdcrmal cavities in this form, exactly the reverse of that 

 in the Aplysinidae, as observed by Von Lendenfeld. 



This is worth mentioning, because in early experiments I 

 found that I had not been caretul to avoid the entrance of 

 accidental particles of carmine after removal from the solution, 

 and also had not subjected the sponges for a short enough time 

 to the action of the carmine mixture, and hence the later stages 

 (of excretion) might easily have been mistaken for early stages 

 of ingestion. I think it therefore possible that, if the Aply- 

 sinidaj of the above-mentioned investigator were left in the 

 carmine for a longer period than is required to complete the 

 metabolic circuit, the sections following this experiment might 

 equally well be interpreted as indicating that the carmine 

 particles were absorbed by the choanocytes and ejected by 

 the subdermal amoeboid cells. 



Lendenfeld certainly seems to write with great conviction, 

 but some of his sponges appear to have been left for a long 

 time in the carmine, e. g. as much as a quarter of an hour. 

 It is remarkable in what an exceedingly short time the particles 



