PROTRUDED BLADDERS. 263 



roughened column, then slowjy distend again, when 

 the orifices are seen to have not changed. 



It is at these orifices of the protruded bladder that 

 the current from within is poured forth, carrying with 

 it the foecal residua of the assimilated particles, and 

 any light floating atoms that may be in the vicinity, 

 as we see with admirable distinctness, by ming- 

 ling with the water a little paint or a minute quantity 

 of powdered chalk. It is then very interesting to 

 trace the particles that are vomited forth, all up the 

 interior of the bladder its perfect transparency 

 allowing them to be clearly discernible from their 

 first issue out of the pit, till, rolling over and over in 

 their course, they are shot out of the extremity of the 

 bladder, and involved in the ever-mingling currents. 



The bladder in this case manifests much more 

 sensibility than that in the Eoseate kind; for, on 

 being touched with the point of a needle, it imme- 

 diately wrinkles and shrinks up, though it does not 

 retract itself, and presently dilates and distends again. 

 It is, therefore, not true that the Sponges manifest no 

 movement or contraction under the impact of ex- 

 traneous bodies, which might indicate the slightest 

 perception of touch. The spongy mass, indeed, does 

 not shrink, and probably this has been generally the 

 only part tested, the extremely delicate protusile 

 membrane having been overlooked. With such ex- 

 periments as I am describing, however, Sponges will 

 exhibit with great distinctness two characteristics of 



