400 Inclusion of Foreign Bodies hy Sjyomjes. 



Cliona to the action of amoeboid cells at its surface ; so that 

 the foregoing suggestions are not without precedent, and, 

 seeing that amoeboid action witliin the sponge-body is well 

 established, it would not be surprising if in such lowly 

 creatures it should also occur at the outer surface. 



Fig. 5. 

 !ExCerna,Z suryixce 



T~=. • <f : 



From the cortex of Eiispongia officinalis, var. rotunda, 

 s, foreign spicule fragment. 



When I wrote the foregoing remarks I was unaware that 

 the subject Lad already been discussed. The following state- 

 ment of the position of the discussion is taken from von 

 Lendenfeld's ' Monograph of Horny Sponges,' 1889, p. 768 : — 

 "... The sponge selects from the material deposited [by 

 currents and waves] such particles as it requires, and allows 

 them to sink into the skin. Haeckel originally assumed that an 

 active selection took place. This was contested by Schulze, 

 who w^as of opinion that the selection, about the existence of 

 which there cannot be any doubt, was not active but passive, 

 and he compared the differences in the size and nature of the 

 foreign bodies in different sponges and their uniformity in 

 one and the same specimen with an ordinary sedimentary 

 process, as the deposit of rough gravel in one part of a river- 

 bed and the deposit of tine sand in the other. If Schulze's 

 hypothesis be correct, that the nature of foreign bodies in 

 sponges is the result of (1) the physical properties of the 

 sponge, and (2) the circumstances of its surroundings, then, 

 of course, tiie nature of the foreign bodies would change if the 

 surrounding circumstances (premiss 2) changed. But this is 

 not the case. In whatever circumstance the sponge grows 



