





44 



THE SPONGES. 



The stalk enlarges at its upper end, where it passes into the body. 



Its 





living 

 Hyali 



specimen 



connection with the body is always excentric, and except in two specimens 

 oblique, as shown in the figure. In the two cases referred to, the rem- 

 nant of the stalk projects vertically from the body. The body itself is 

 heavy, and because of the numerous canals perforating it, is easily torn. 

 The stalk is firm and hard, except in its uppermost region. Here, where 

 there are no synapticula between the principal supporting spicules, it is 

 comparatively soft and easily broken, although in the 

 doubtless flexible. The attachment of the stalk to the 

 spicules shows that the body itself cannot, in the natural position, be far 

 from the surface layer of mud. And this fact, taken together with the 

 character of the uppermost part of the stalk, suggests that the disc rests 

 upon the surface mud, something after the fashion of a Renitta, instead 

 of projecting freely in the water. 



Both surfaces of the body exhibit the apertures of very numerous 

 canals, which pass vertically into the interior. They are about equal in 

 abundance and size on the two surfaces, being smallest in the peripheral 

 region. The diameter of the apertures ranges from less than 1 mm. to 



* 



2 mm., or in some individuals to 4 mm., and on both surfaces they are 

 covered in by the dermal and gastral membranes respectively. The axial 

 canal in the stalk is | to \ the diameter of the stalk, widening greatly above 

 where the stalk passes into the body, and opening into several smaller 

 canals. In two specimens examined these canals pursued so intricate a 

 course that I could not trace them to their openings. In another speci- 

 men the canals were larger and opened on the gastral surface, as described 

 by Schulze for Caulophacus lotus (1887, p. 124) and C. agassizii (1899, p. 37). 



As in the other species of the genus, the principal parenchymalia 

 are hexacts and diacts. The hexacts are distributed through the body 

 of the sponge, where they are abundant but not crowded (Fig. 10, Plate 5). 

 In the stalk they are few in number, and those seen lay outside the main 

 diact skeleton. The hexacts are rather slender, with straight or gently 

 curved rays which are often accompanied by a few diacts. The rays are 

 smooth, taper evenly to rounded points, and in general are equal or 

 subequal, measuring 700-1200 /x x 28-48 /x. Rarely hexacts are found 

 in which all the rays are covered with sharp microtubercles. Such spicules 

 seem to be modifications of the hypodermal pentacts. 



The diacts of the body are slender, straight, or slightly curved; in 





















