and Functions of' the Sponge, 127 



pores ill most of the other species. I was therefore led to sus- 

 pect that the currents are not caused by polypi on the surface, 

 but by ciliae, or some similar apparatus, placed around the en- 

 trance of the pores, or on the margins of the gelatinous net- 

 works, or on the whole surface of the internal canals. I first 

 placed a thin layer from the surface of the S. papillaris^ in a 

 watch-glass with sea water under the microscope, and, on look- 

 ing through its pores, I perceived the floating particles driven 

 with impetuosity through these openings, they floated with a 

 gentle motion to the margin of the pores, rushed through with 

 a greatly increased velocity, often striking on the gelatinous net- 

 works, and again relented their course when they had passed 

 through the openings. The motions were exactly such as we would 

 expect to be produced by ciliae, disposed round the inside of 

 the pores ; but the most intense observation, with high magni- 

 fying powers, did not render cihae visible on this or any other 

 species which I examined. I now took deeper sections from 

 the substance of a great variety of living sponges, after remo- 

 ving their surface, and on examining them in the same manner ,^^ 

 under a powerful microscope, I found that, wherever a portion 

 of an internal canal presented itself, there was a distinct and 

 rapid current through it, but the moving organs were as little 

 distinguishable on these, as on the margins or net-works of the 

 pores. On looking with the microscope through the pores of a 

 detached portion of the S. compressa^ (fig. 23. J,) I have some- 

 times observed a confused motion among the granular bodies 

 lining their sides, and have even seen these monade-like bodies 

 in groups staggering to and fro, when they had fallen separate 

 to the bottom of the watch glass. But, although every known 

 analogy would lead us to believe that these motions and the 

 currents are produced by ciliae, I have never been able, by any 

 artifice, or by the highest magnifying powers, to bring them 

 distinctly into view in any species of sponge. 



What relates to the formation, expulsion, and development 

 of the ova, I shall exemplify chiefly by what I have observed 

 during three successive winters in the *S'. panicea, adding at the 

 same time such peculiarities as I have remarked in other spe- 

 cies. By dividing this memoir into parts, and thus protracting 

 its publication, I liave been enabled to vary and repeat my ex- 



