ON MEKLIA NORMAXI. 663 



A living sponge broken in half — i. e. in vertical section — 

 shows (PI. 32, fig. 10), beneath the soft surface-layer, a more 

 or less regular white calcareous honeycomb, with blocks of 

 reddish orange-coloured jelly iiiling in the spaces, the appear- 

 ance being that of pots of jelly superposed one on another in 

 from one to three or four or, rarely, five storeys from edge to 

 centre of the sponge. The blocks often form fairly regular 

 horizontal and. vertical rows. Occasionally the uniformity of 

 a vertical row is interrupted by a block of double breadth, 

 and very frequently the regulai-ity of the horizontal rows is 

 broken owing to the blocks of " jelly " being longer or shorter 

 than the average. PI. 32, fig. 9, shows variation both in the 

 length and (once) in the breadth of the blocks of soft tissue 

 filling in the spaces or crypts in the calcareous skeleton. PI. 

 35, fig. 17, shows a section of the skeleton with nearly equal 

 and uniformly arranged, compartments. In the youngest 

 specimens, which form little red spots only 2 or 3 mm. in dia- 

 meter, there are no crypts at all, the calcareous skeleton con- 

 sisting merely of slender bars of a wide-meshed polygonal 

 network. Also, in the case of specimens which can extend 

 freely over the flat or curved, smooth inner surfaces of old 

 bi-valve shells, there may be only a few crypts in perhaps 

 one or two storeys at the centre of the crust, the rest of the 

 skeleton being composed of deeper or shallower pits, with 

 the floor formed by the surface of the shell. 



Not infrequently the sponge grows in depth rather than in 

 extent, and the crypts may then become four, or even five, 

 storeys deep, or rather, it should be said, high, for the growth 

 is from below upwards. In such specimens the storeys may 

 diminish gradually to four, three, two, one, and finally to 

 none at the growing edge. 



On viewing by powerful reflected light under a low magni- 

 fication a stained specimen in glycerine, it is possible to see, 

 below the transparent surface, circular masses of flagellated 

 chambers filling in the uppermost spaces of the calcareous 

 framework, and joined to each other by radiating spokes, 

 also composed of masses of flagellated chambers, crossing 



