120 JOURNAL OF THE [May, 



successive buddings, a colony of a shape more or less globular. 

 In other words, the sponge takes on the figure with which we are 

 familiar, with pores throughout the mass, and exhibiting at or 

 near the centre the osculum of the original sponge. Sometimes 

 two large oscula are seen, corresponding to two growths, one of 

 which branched off early from its companion. The ventriculi, 

 old and young, of the entire colony, are in free communication 

 with one another. In general it may be said that the water goes 

 in on all sides and goes out on all sides, but tends to pass out by 

 different openings from those by which it came in. 



The foregoing description presents the sponge simply as a 

 porous mass of sarcode cells. In other examples spicules are 

 found attached to the outside wall in numbers so great as to 

 invest it completely. These may assume every variety of shape 

 and size, and are often of great beauty. Some are needle-like ; 

 others have the form of a three-pointed star ; still others are 

 crescent-shaped, with a long spur projecting from the middle of 

 the convex side. These all interlock in such manner as to 

 form a strong and complete net-work in the outer tissue of the 

 sponge. Only occasionally do they extend through all the 

 tissues. 



But in this form the sponge is of no practical service. To be 

 useful, it must be free from spicules and must have a framework 

 of keratose. Where, then, and how is the keratose deposited ? 

 Some sponges have a layer of cells between the inner and the 

 outer layers ; in other words, mesoderm, as well as endoderm 

 and exoderm cells. The keratose is generally formed as a mass 

 of fibres interlacing in all directions through the mesoderm layer, 

 and sometimes also embracing and thus firmly uniting the inner 

 and the outer layers. The result of this growth in a sponge of 

 this kind is that every canal in the whole sponge becomes in- 

 closed in a tube of keratose, so that the keratose of the entire 

 communal animal constitutes a framework of the same general 

 form with the animal itself. Now, should you pluck a living 

 sponge, of this variety, from its anchorage, you would find it 

 feeling soft and slimy in your hand. The slimy substance is 

 simply the sarcode of the exoderm cells, which envelops the 

 whole sponge. The inner walls have also their layer of living 

 cells. But the dealer in sponges wishes them rid of their sar- 

 code. Accordingly, when the sponges are gathered from the 



