128 
THE VOYAGE OF H.M.S. CHALLENGER. 
attain a diameter of 0’25 mm., and are chiefly composed of cells in a non-granular 
state, consisting of deeply stained protoplasm somewhat vacuolated ; some of the 
constituent cells, however, consist of unstained finely granular material, and similar 
colourless granular cells occur separately scattered amidst the fibrous tissue of the 
cluster-bearing zone. 
Choanosome. — Amidst the deeply stained sarcenchyma of the mesoderm are 
numerous scattered cells, each lying in a small cavity, caused probably by post-mortem 
shrinkage. These cells are of various sizes, the largest about 0'02 mm. in diameter, and 
they consist of deeply stained, finely granular protoplasm, enclosing a well-marked oval 
nucleus about O’Ol mm. in length, and in this again is a small spherical nucleolus about 
0’002 mm. in diameter. Besides these cells are others similar, but consisting of a 
network of unstained material bearing minute stained granules on the nodes ; these 
appear to result from exhaustion of the stained cells. 
The flagellated chambers vary from about O'OIG by 0’02 to 0'02 by 0*024 mm. 
in length and breadth. 
Chones. — The chones have the irregular canal-like form common in the genus. The 
cortex immediately adjacent to them is somewhat modified, forming a thin layer next the 
lining epithelium less fibrous than elsewhere ; in the homogeneous matrix of this layer 
minute fusiform cells about 0*04 to 0*07 mm. long appear, they lie with the long axis at 
about right angles to the lining epithelium, against which the outwardly directed fibril 
terminates ; the fibril of the opposite extremity is lost amidst the fibrous tissue of the 
cortex. 
The chiasters, which are rare, are best observed in superficial tangential sections of the 
cortex, where they will be found in comparative abundance immediately below the 
epithelium around the margin of the pores. 
Pilochrota crassispicula, Sollas (PI. XIV. figs. 9-15). 
Piloehrota crassispicula, Sollas, Prelim. Account, Sci. Proc. Roy. Dubl. Soc., vol. v. p. 190, 1886. 
Sponge (PI. XIV, fig. 9), irregularly spherical, about 3*5 cm. in diameter, free, numerous 
foreign bodies attached to the surface by strong fibrous bands, a single large oscule at the 
summit, with a membranous margin, leading into a long tubular cloaca, which descends 
obliquely into the sponge ; excurrent canals opening in the walls of the cloaca by numerous 
mouths, spun over by a coarse reticulation, each mesh of which is occupied by a sphinctrate 
velum. Pores in sieves, overlying chones ; situated chiefly at the bottom of narrow 
grooves, which form a network of depressions over the surface, giving it a kind of 
embossed appearance. 
Spicules. — I. Megascleres. 1. Oxea (PL XIV. fig. 10), a massive, straight or curved, 
fusiform variety, sharply pointed, or pencil pointed, or rounded off near the point, 2*3 
