CHAUNOPLECTELLÄ. CAVERNOSA. 6l 



sj)iculation of the septal wall as seen in a section, a parenchymal 

 tauactin is seen to send out beyond the surface its short unpaired 

 ray, which, like the outstanding rays of canalar oxyhexactins, is 

 supplied with a sigmatocome at the tip. 



In small specimens of the species, such as are shown in fig. 

 9, PI. v., all the parenchymal hexactins, which are certainly 

 never so large as in full-grown individuals, are nearly regular in 

 form. In most of them the rays are almost straight or but 

 little bent, and do not show striking differences in their length. 

 Spicules with 3-5 rays are not present or are, at any rate, quite 

 scarce, so that the parenchymalia may be said to consist largely 

 at least, if not entirely, of hexactins and diactins. 



The parenchymal diactins are represented by all sizes, from 

 those of the dimensions of ordinary comitalia up to those with a 

 length of 12 mm. and a breadth of 50/^- in the middle. But the 

 thickness never reaches the degree attained by the rays in some 

 hexactins. The center is sometimes externally marked by an 

 annular swelling, but more generally it is not. The diactins are 

 disposed either more or less isolatedly or in bundles, generally 

 in company with other kinds of parenchymal spicules. They are 

 relatively few in number in the main body of the sponge, where 

 by far the greater part of the- parenchymalia consist of spicules 

 with more than two rays. The relative proportion becomes 

 however gradually reversed in the lower region of the body. 

 Here, but more especially in the stalk-like base, the parenchymal 

 fibers form anastomosing bundles of very considerable thickness 

 and of exquisitely silky appearance (see PI. V., fig. 10). The 

 elements of these bundles are preponderatingly diactins, inter- 

 spersed amongst which ure found small slender-rayed hexactins. 

 The diactins at the inferior end of the bundles are inserted 



