116 THE SPONGES. 



stratum or cortex is about 700 /x thick, very dense and firm, lighter in color 

 than the interior. 



The pore areas (Fig. 1, Plate 21) are free of spicules; irregular in 

 shape; many long, narrow, and meandering; others rounded. Pores them- 

 selves not discernible in surface view, probably closed. Immediately below 

 the dermal membrane of the pore area may be seen, on focussing, the 

 rounded optical sections of small pore canals 20-30 fx in diameter. In 

 radial sections there may be seen in the cortex numerous branching canals. 

 These connect with the narrow pore canals, which extend outward in a 

 more or less radial direction tow^ard the surface. The cortical canals are 

 especially conspicuous beneath the mammillary protuberances (Fig. 6, 

 Plate 16 ), where they communicate with the canals of the interior 

 through narrow apertures, each of which perforates a protuberance which 

 projects into the cavity of the internal canal (Fig. 6, Plate 16). Very 

 probably the protuberance is produced by the contraction of a sphincter 

 guarding the aperture, the apparatus being chone-like. 



The cortex or ectosome is collencliymatous. No flagellated chambers 

 were observed in it. In the remainder of the sponge (choanosome) the 

 chambers are thickly packed ; mesenchyme of the choanosome, collen- 

 chymatous. The flagellated chambers are longer than wide, about 32 /x 

 in transverse section. The collar cells are long and slender; the trans- 

 parent collar longer than the opaque basal jDart of the cell ; total length 

 of the cell, including the collar, about 10 fx. Very frequently the central 

 ends of the collars are connected in an irregular fashion, as if artificially 

 glued together. 



Sjjicules. 



1. Sfi/lc, Fig. 5 h, Plate 16 ; smooth, straight, tapering toward both 

 ends so as to be fusiform ; pointed end sharp and slender ; basal end 

 simply rounded off without enlargement. Size, 1580 /x x 36/Lt to 1020 /xx 

 28 fx. Abundant. 



2. T/jlostf/le, Fig. 5«, Plate 16; smooth, straight, stouter than the 

 style; fusiform and sharp-pointed; basal end tapering more than the 

 pointed end and capped with a distinct rounded head. Size, 850 /u, x 38 /x to 

 765 /x X 32 /x. Abundant. 



J. Ti/losif/le, Fig. 5 c, Plate 16 ; similar in shape to the large tylostyle, 

 with which it is connected through intermediate sizes. Size, 280 /x x 12/x to 

 124 ^ x 5 /x. Abundant. 



