BV £. F. KALLMANN. 33 < 



The main skeleton is a coarse, irregular, reticulation of very 

 stout fibres, oftt-n exceeding 30U /x in thickness, composed of 

 densely packed strongylote and substrongylote spicules un- 

 ccniented by spongin. The meshes of the reticulation, which 

 are usually more or less rounded in outline, are of very vari- 

 able width, averaging, say, 500 /x. Within the meshes are 

 abundant scattered spicules, which sometimes form rather 

 dense masses ; these spicules for the most part arc similar to 

 those forming the fibres, but comprise also fairly numerous, 

 slenderer, oxeote spicules of a distinct kind. At the surface, 

 the outermost transverse fibres of the main skeleton constitute 

 a subdermal reticulation that extends horizontally immediate- 

 ly beneath and in contact with the dermal membrane. The 

 dermal membrane is provided with numerous horizontally 

 directed oxea (similar to those scattered in the choanosome) 

 which in general are arranged reticulately, forming meshes of 

 about 120 fj, in diameter. Where the membrane overlies the 

 interstices of the subdermal reticulation, it is pierced by round 

 pores, each of which singly occupies one of the meshes of the 

 dermal reticulation. 



Spicules.— (b). The strongyla are more or less curved, 

 range in length from (rarely) less than 40 to about 280 //, and 

 attain a maximum diameter of 17 /x; the shortest have an ave- 

 rage stoutness of about 7 /x. Generally speaking, the longer 

 spicules are less curved than the shorter, and are less bluntly 

 rounded off at their extremities, so that very often they might 

 more correctly be termed sub-strongyla, or even, at times, sub- 

 oxea. Also, the shorter spicules are often somewhat angulately 

 curved. Of the longer spicules, an occasional one is asymmet- 

 rical with regard to opposite ends, approximating to the form 

 of a bluntly pointed stylus. 



((f). The oxea also are more or less curved, though usually 

 in less degree than the strongyla : and their curvature likewise 

 is often slightly angulate. The greater degree of curvature 

 and of angularity of curvature are, however, as in the case of 

 the strongyla, more frequently shown by the shorter than by 



