Excretori/ Processes in Port f era. 



491 



fomily ehar^'t'd witli a lair amount of niimite carmine 

 grains. 



The late of the loadcil amccboiJ cells can be easily followed. 

 In sections of colonies which were killed as late as or later 

 than five minutes from the time of removal from the carmine 

 (or seven minutes from the first immersion in the latter) 

 the ectodermal outline is seen at places to be interrupted, as 

 in fig. 2 or fig. 4, by a protrusion of the mesodermal substance 

 to the exterior, with the appearance of a volcanic crater, and 

 at some of these points are clearly seen a number of amoeboid 

 cells, which we may term " nephrocytes," charged with 

 carmine particles and evidently in the act of leaving the 

 sponge. 



Fig. 5 shows a pair of these cells which were free in the 

 paragastric cavity, seen under high power. 



Fig. 4. 



Fiff. 6. 



Fig. 5. 





Fig. 4. — Mass of nephrocytes escaping from ectoderm. 

 Fig. 5. — Mass of nephrocytes free from colony. 

 Fig. 6, — Amoeboid digestive cell. 



These are mesodermal cells or metamorphosed choano- 

 cytes (it is obvious that it is quite impossible to pronounce 

 definitely whether they are really the actual clioanocytes 

 which ingested tiie carmine in the incurrent canals), which 

 are destined, upon the processes of digestion being completed, 

 to leave the colony, carrying with them the solid waste 

 products of excretion. We have here an example of a process 

 of intracellular excretion for the removal of waste solids, 

 quite distinct and apart from the liquid excretory processes 

 which doubtless take ])lace through the medium of the water- 

 currents caused by the clioanocytes. 



