209 



Organ. Function. Ph ylogenetic Origin. 



Stomodaeum Ingestion Ectodermal 



Enteron Digestion Endodermal 



Proctodaeum Egestion Ectodermal 



Ontogenetic Origin. 

 Epiblastic. 

 Hypoblastic. 

 Epiblastic. 



The want of certainty with regard to the Phylogenetic origin of 

 the polycytic anus obscures also the history of the proctodaeum. 



It has been seen that in the Metazoa monocytic ingestion consists 

 not only of an ingestion of food particles into the substance of the cell, 

 as in the Protozoa, but also of the subsequent immigration of the cell 

 to the interior of the organism: in the monoblastic form into the 

 segmentation cavity and in the diploblastic organism, into the «meso- 

 gloea((. In a precisely parallel manner the monocytic egestion as 

 occurring in the Metazoa consists not only of the ejection of the indi- 

 gestible residue from the cell as in Protozoa, but of the expulsion of 

 the whole cell with its contents from the organism. This process ap- 

 pears to be one of very general occurrence in the Metazoa and is an 

 important factor in the determination of their morphology. It is quite 

 distinct from the excretory processes ^3 and the emigrant cells should 

 be known either as egestive cells or ek-phorocytes and not as »ne- 

 phrocytes«: many so-called excretory organs appear to belong truly to 

 the monocytic egestive function. 



In studying the monocytic egestion one need not necessarily follow 

 out the whole metabolic circuit, for although normally ingestion takes 

 place, in diplo- or triploblastic forms, at the endoderm layer, yet the 

 ingestive cells are to be found in the interior (coelom) and if foreign 

 particles be introduced, artificially, into the coelom, the seat of mono- 

 cytic digestion, they are got rid of by the organism by the normal 

 egestive methods. 



These experiments have not been conducted for all the metazoan 

 types of organism but sufficient data are to hand to show a parallel 

 series to the ingestive processes. 



23 It is however quite likely that in many cases the ek-phorocytes will give 

 reactions indicating the presence of excretory liquids in them. It is possible that the 

 organism may make use of these cells to carry away its excreta (cf. autumnal leaves) 

 just as later it makes use of the egestive current in Coelomata, but it must also be 

 remembered that the ek-phorocytes themselves are masses of disintegrating proto- 

 plasm, and de facto abounding in liquid nitrogenous excreta. 



