E. 3IAESHALLI. — AECHJEOCYTES. 165 



If I am right iu the above assumption, tlie Hexactinellids 

 are to be regarded as a group of sponges, whicli have undergone 

 a far-reaching development and differentiation in the spicules, but 

 have remained in a jirimitive condition so far as certain points 

 in the soft parts are concerned. How far this view, which is of 

 great consequence to the systematic position to be assigned to 

 the Hexactinellida, will be borne out or contradicted by a more 

 extended knowledge, remains to be seen. 



Cells in connectiox with teabecul.e. — As such are to be 

 mentioned in the first place the small cells to which reference 

 has been already made under the name of ' archseocytes.' 



Archccocyles. 



(PI. V, figs. 36, 37, 39, 43; arch). 



This term was, so far as I know, first used by Sollas 

 (' Sponge ' in the Encyclopedia Brittanica) as an equivalent for 

 amoebocytes. I hold it exceedingly probable that the cells now 

 under consideration correspond both morphologically and physio- 

 logically to the amoebocytes of other sponges. However, being 

 in want of definite knowledge as to whether they are similarly 

 capable of amoeboid motion, I have preferred to designate them 

 by a term of more indifferent signification in that regard. I 

 believe, at any rate, that in the archseocytes of the Hexactinellida 

 we have a kind of cells which remain iu a low state of histolo- 

 gical and functional differentiation, retaining to a certain degree 

 the blastomeric character, and which give rise in the adults 

 at times to the thesocytes and at times to reproductive ele- 

 ments. 



The archseocytes in E. marshalli, and also iu many other 



