AKT. 12 



HEXACTINELLID SPONGES OKADA 



35 



extraordinary variability in length, but is usually 3.5 mm long 

 and 12;ti broad at the middle. It is disposed obliquely or perpen- 

 dicularly to the surface, traversing the wall of the tube in a radial 

 direction, the proximal two-thirds imbedded in the body of the 

 sponge. Though the tip does not usually penetrate the dermal mem- 

 brane, it occasionally does for a third of its length. The inner 

 weaker and pointed ends remain at some distance from the gastral 

 membrane or reach it. The spines arranged around the shaft are 

 very slender and short, supported on very weak bracketlike processes. 



Figure 5. — Farrea watasei, ntw species : a. Dermal pentactin ; b, hexactin ; c, 

 discohexaster (form A) ; d, discohexaster (form B) ; e, oxyhexaster ; f, oxyhex- 

 aster ; g, circular umbollate clavulae ; h, anchoratG hooked clavulae ; i, ancliorate 

 hooked clavulae ; j, anchorate hooked clavulae. All X 250 



Besides the uncinates, parenchymalia are represented by simple 

 oxyhexasters (fig. 5, /) in abundance, though they frequently occur 

 in subdermal or subgastral regions, intermingled with discoctasters. 

 In these the principal rays, which are long, smooth, and some- 

 what attenuated to the end, divide into two to three widely diverging, 

 straight, short, smooth terminals, half as long as the principals. 

 Terminals arising infrequently from the principals are reduced to 

 only one in number (fig. 5, e). In certain cases one of the six rays 



