sponge-fauna of Norway. 443 



rounded off at tlie ends, so that, instead of being long, 

 slender, and pointed, they become short, thick, and stumpy. 

 The proximal end of the shaft is sometimes rounded off in 

 the same way. 



(v.) The grapnels (PI. XVII. fig. 4) are distinguished by 

 their long, sharp, usually straight rays, but there is great 

 variation among them in this and other respects ; in one form 

 (fig. 4) the head of the shaft is scarcely at all thickened, and 

 the long rays start with a wide outward sweep ft-om it (at an 

 angle of 55° to 60°) and then somewhat abru]Dtly turn back- 

 wards and run more nearly parallel with it, frequently at an 

 angle of 18° to 20° ; in another form the shaft thickens 

 towards the head, which is thick and long, and the rays form 

 only short, stout, widely-diverging prongs (PI. XVII. fig. 14) ; 

 but there is every intermediate form between these two, and 

 many minor variations surrounding them ; in the expansion or 

 not of the shaft below the head, in the size and form of the liead, 

 in the length of the rays and the angle they form with the shaft, 

 there is great variety ; by far the commonest form, however, is 

 that shown at fig. 4, or some close approach to it. Those grap- 

 nels which lie entirely within the body are often O'l inch long- 

 in the shaft, with rays 0'0082 inch long ; those which extend 

 beyond it have not yet been observed entire, but have been 

 measured up to 0*34 inch in length, and probably in the entire 

 state they are sometimes not much shorter than 1 inch. 



The development of the grapnels will be described in treating 

 of the young forms of the sponge. 



(vi.) A not uncommon variety of large spicule remains to 

 be noticed (PI. XVII. fig. 3) ; it resembles the shaft of a 

 tern ate spicule, but instead of dividing it thickens club-like 

 at the distal end ; in some cases (fig. 17) a protuberance repre- 

 senting a rudimentary ray occurs on one side. These spicules 

 call to mind the club-shaped forms of Rhaphidotheca Marsltall- 

 Hallij and are either young forms of ternates, or ternates in a 

 state of arrested development, or abnormal forms of the fusi- 

 form acerate spicule. 



(vii.) The smallest of the minute spicules are the spini- 

 spirulaj (PI. XVII. fig. 24) ; these consist of a straight or 

 curved shaft, from which spines arise along a spiral course 

 and project radially ; the spines are usually sharp-pointed and 

 smooth, but frequently also very finely roughened all over, often 

 with quite abruptly truncated ends. The shaft sometimes be- 

 comes very short ; and then the spinispirula is scarcely distin- 

 guishable from a minute stellate. 



(viii.) The larger minute spicule appears to be a spinisjurula 

 reduced to a very simple form {v. Kent, vii. figs. 16, 17, 18). 



