REPORT ON THE HEXACTINELLIDA. 253 



delicate pinules with thin pointed basal rays, and with slender pointed free radial, as we 

 have already described in the outer skin (PI. XLVI. figs. 10, 11). 



There is in the gastral skin a very abundant occurrence of large and long amphidiscs, 

 with short, hemispherical, eight-rayed umbels, and tubercled, moderately slender, axial 

 rods (PI. XLVI. fig. 11), such as occurred sparsely in the dermal membrane. More abun- 

 dant are the small, long amphidiscs, with slender, roughened axis rod, and short, hemi- 

 spherical, eight-rayed terminal umbels. 



The canalicular skeleton of the larger efi'erent passages differs essentially from that 

 of the afferent ducts of the lacunar subdermal or subgastral spaces. Even macroscopic 

 inspection of the internal surface of these canals and lacunae, one notices a marked 

 difference in the character of the surface, which is in the efferent canals quite rough and 

 villous, while that of the afferent canals, and of the subdermal or subgastral lacunae, 

 appears comparatively smooth, or only exhibits a fine uniform roughness. On all the 

 larger canals and lacunae, the walls are supported by strongly developed hj^ocanalicular 

 oxj'pentacts, with rays varying in strength, according to the size and wid.th of the canals. 

 Between the larger hypocanalaria, smaller forms always occur. The peculiarly rough 

 nature of the afferent canals is conditioned by especially long, though not particularly 

 broad autocanalicular pentact pinuli, in which the freely projecting cypress-like ray 

 attains a length of 0*4 mm. and more. Of course between these long pinules shorter 

 forms occur, with slender, slightly spinose, free radial rays (PI. XLVI. fig. 6). Isolated 

 amphidiscs of the larger sort and numerous representatives of the smaller type occur in 

 the skin of the wider efferent canals (PI. XLVI. fig. 6). Both the number and the size 

 of the canalicular pinules and amphidiscs gradually decreases with the width of the 

 canals, until they finally disappear in the neighbourhood of the chambers. 



The lining layer of the large afferent canals and of the subdermal spaces is supported 

 by smooth hypocanalicular oxypentacts entirely similar to those of the efferent canals. 

 Both the autocanalicular pinuli and the amphidiscs are, however, entirely absent 

 (PL XLVI. fig. 7, left). 



The pleural prostalia, which project for 3 to 6 cm. from the lateral wall of the 

 sponge, are strong smooth needles, which attain the thickness of a millimetre. They run 

 to a point within the body, but the external termination unfortunately eluded distinct 

 observation, since they were almost all broken off. Doubtless, however, they are 

 either smoothly and simply pointed, or are terminally toothed, and end in a small 

 five-pointed club. The same is true of the marginalia, which project for about 

 3 to 4 cm. I have abeady mentioned that numerous long uncinates with pointed 

 external extremities project between the pleural prostalia. 



The long basalia, which issue like the pleuralia in bundles, but become woven into a 

 felted basal tuft, begin like the pleuralia and marginalia in an internal pointed end, swell 

 out beyond the body into smooth cylindrical beams, which again decrease in thickness 



