ZOOPHYTES. 405 



flexible, it contains solid elements. Just below the 

 expansion ot' the tentacular blossom, we see imbedded 

 in the skin a vast aggregation of calcareous spicula. 

 Individually, these are very minute, and their form is 

 swollen in the middle, and taper at each extremit}', 

 the whole roughened with projecting knots. Collec- 

 tivelv, they are grouped in regular forms, crowded 

 into dense masses at the foot of each tentacle ; the 

 mass having a three-pointed outline, of which the 

 central and largest point runs up into the tentacle. 



Towards the lower region of the column, spicula 

 again occur, scattered throughout the skin, and crowd- 

 ed into groups, one on each interseptal space. These 

 spicula are of a very different shape from the upper 

 ones ; for they form short thick cylinders, with each 

 end dilated into a star of five or six short branches, 

 which are again starred at their truncate ends. 



If we now sacrifice our little Cow's pap to our 

 scientific curiosity, we shall see something of its in- 

 ternal structure. When removed from the water, the 

 blov.'er-like poh'pes soon retract. I now cut open 

 the mass lengthwise with a keen knife, and you see 

 that it is permeated by canals I'unning from the base 

 towards every part of the circumference, dilating here 

 and there to form the cells which protrude and retract 

 the polypes. This is a complete system of water- 

 supply : the surrounding sea- water entering at the 

 mouths of the several polypes, bathes the whole 

 interior, and conveys oxygen and the products of 

 digestion together to every part of the compound 

 organism. 



The fleshy substance which surrounds these canals 

 is of a loose spongy character, and grates beneath the 



