440 Prof. W. J. Sollas on the 



sponge exceedingly well nourished and abounding in proto- 

 plasmic structures ; and y&i, when we come to study its histo- 

 logy, we shall find that it is distinguished, in marked contrast 

 with the Corticatffi, by the small proportion of its protoplasmic 

 contents, the great mass of the sponge consisting of a gelati- 

 nous matrix wliich, whatever its composition may be, is 

 certainly something very diflerent from proto])lasm. The 

 rapidity of the water-streaming is therefore probably connected 

 with the poverty in food-particles of the surrounding water, a 

 great deal of water having to pass through the sponge in order 

 to afford it sufficient nourishment. 



The sphincters probably act as regulators to the water- 

 streaming, checking it when the water is more than usually 

 burdened with suspended particles, allowing it freer passage 

 when food is scarcer. They might also govern its distribu- 

 tion, closing the passage in some directions, opening it in 

 others, though, in the presumed absence of a combining appa- 

 ratus such as a nervous system would furnish, this seems 

 unlikely. 



In connexion with the '^wide-openness" of the canal-system, 

 the small size of the oscule is worthy of note. It seems to 

 point to a rapid escape of the outflowing water, and its con- 

 sequent ejection to a considerable distance from the inhalant 

 surface. The relative size of the poral and oscular areas in 

 different sponges has never yet been made the subject of in- 

 vestigation, although it differs greatly in different species, 

 and must stand in close connexion with the physiology of the 

 water-streaming system. As a beginning, I have attempted 

 to determine, in the case of this sponge, (i.) the ratio of the 

 poral to the superficial area, and (ii.) the ratio of its total 

 poral area to its total oscular area. In order to make the first 

 determination, a specimen was taken from spirits and allowed 

 to drain till the edges of the open pores just became visible ; a 

 part of the surface with its pores was then accurately sketched 

 with the aid of an oblique reflector and under a magnification 

 of thirty diameters. We shall not need to trouble about the 

 absolute size of the pores, as we are only about to determine 

 a ratio. A given area of the drawing was next taken, and 

 the area of the pores in it calculated. I give the results 

 obtained in two instances. In the first — 



(i.) The area of the sjDonge-surface taken from the sketch 

 was 6 square inches. 



(ii.) It contained sixteen pores, of which two had a dia- 

 meter of 0*3 inch, two of 0*25, two of 0*22, eight of 

 0-2, and two of O'l. 



