CHAUNOPLECTELLA SPINIFERA. 73 



While many exhibit rays about 2 mm. long and 40/^ broad near 

 the spicnlar center, others are smaller, leading down to those 

 which are one-fourth the size just mentioned or even smaller. 

 Occasionally ^xe meet with very small and fine-rayed hexactins, 

 measuring 200 f^ or less in ray-length and only about 2/^ in breadth 

 of rays near the center. In one and the same parenchymal 

 hexactin the rays are frequently of markedly unequal length. 

 They are sometimes nearly straight, at other times somewhat bent. 

 They are usually smooth throughout and taper gradually towards 

 the sharply pointed end. See PL VI., fig. 8. 



The diactinic parenchymalia play a comparatively less im- 

 portant part in the composition of the parenchyma, though the}^ 

 can not be said to be sparse in quantity. They mostly occur in 

 small loose strands running in company with the rays of hexactinic 

 parenchymalia. In the basal region of the sponge, however, the 

 diactins combine to form bundles of a rather conspicuous strength 

 and seem to constitute the principal mass of the parenchyma in 

 that region. They are long and slender, being mostly under 14 

 /i in thickness, though there occasionally occur much thicker ones 

 among the bundles of the base. The center is externally smooth 

 or else is provided with an annular swelling, rarely with four 

 cruciate knobs. Ends rough-surfaced, usually slightly swollen 

 and conically pointed. 



The gadralia are variously sized oxyhexactiiis which in no 

 way differ from those of the parenchyma. In forming the gastral 

 layer they are loosely and irregularly interlocked with one another, 

 but always projecting one of the rays into the gastral cavity. 

 Diactins are not found in the layer. 



