62 



imperialis. It has the appearance of a rather soft, straight and slightly-inflated 

 tube with circular transverse section. The terminal sieve-plate is only slightly 

 convex and is surrounded by a collar 5 mm. high, which thins out to a sharp 

 margm and is nearly vertical to the axis of the sponge. The slightly attenuated 

 lower end of the body is continued into a root-tuft, composed of a felted mass of 

 spicules. The total length, inclusive of the root-tuft, is about 40 cm. the maxi- 

 mum transverse diameter of the central part of the body is 7 cm. The upper 

 end is 7 cm., the lower end 6 cm. and the root-tuft 4-5 cm. broad. 



The wall of the sponge-tube is 2-3 mm. thick and perforated by numerous, 

 circular parietal apertures with smooth margms. These are situated at the bases 

 of crater-hke depressions of the outer surface. The latter has a reticular 

 structure, whilst the inner surface of the tube- wall appears smooth. The parietal 

 apertures are surrounded by jris-like, annular membranes of varying breadth. 

 Although the position of these apertures is not quite regular, yet one can 

 see, that they are on the whole arranged in longitudinal and transverse rows, 

 crossing each other at right angles, at least m the upper and central parts of the 

 body (pi. XXII, f. 1, 2). 



The size of these parietal apertures, and their distance from each other, 

 increases pretty uniformly from the upper to the lower end of the sponge. Just 

 below the collar surrounding the terminal sieve-plate they are hardly 1 mm. wide 

 and only 2 mm. apart. In the lower part of the body they are often over 2*5 

 mm. wide and 6-8 mm. apart. Between them sharp ridges and crests of vari- 

 able height (3-6 mm. and more) protrude from the outer surface. These extend 

 transversely or obliquely in diagonal, low spirals, more rarely longitudinally, and 

 anastomose frequently; here and there they dissolve themselves into rows of 

 conic protuberances; generally speaking they are very irregularly developed. 

 On the whole these protuberances are higher on the upper and the lower 

 than on the central parts of the sponge. On the outer surface small roundish 

 pores, less than 500 M broad and the same distance apart, the entrances to the 

 incurrent canals, are everywhere visible through the tender dermal membrane. 

 On the inner, gastral surface of the tubes one finds, between the parietal apertures, 

 numerous, small, circular pores of varying diameter, the openings of the excur- 

 rent canals. These do not lie so close together as the incurrent pores of the 

 outer surface. Often one sees a single or double longitudinal or transverse row 

 of such pores up to 1 mm. wide and numerous more irregularly arranged, smaller 

 pores, between the parietal apertures (pi. XXII, f. 2). 



The terminal sieve-plate is convex, watch-glass-shaped and consists, as in 

 all other species of Euplectella of an irregular network of flattened strands, 

 lamellarly extended at some of the nodes. The meshes of this network are 

 irregularly polygonal, more rarely rounded, and 2 to 5 mm. wide (pi. XXII, 

 f. 8). 



