76 SYNOPTIC COLLECTION. 



tral hollow. In Hyalonema sieboldi Gray (No. 69), the 

 cup-shaped body is supported on a long tuft of silicious 

 spicules, by means of which the animal is anchored in 

 the mud. These rooting spicules are sometimes two feet 

 long, while the spicules of the body are varied and beau- 

 tiful in design. 



The probable ancestor of Euplectella speciosa Q. & M., 

 was one of the Dictyospongidae which were vase-shaped 

 sponges composed of spicules that united to form a frame- 

 work similar to that of Euplectella. This has disap- 

 peared from the fossils but the tracery of the fibers may 

 be seen on their surfaces. In the living Euplectella (No. 

 70) the delicate skeleton is covered by a grayish brown 

 fleshy matter and skin. It is interesting to note that the 

 young Euplectella has the spicules separated, but with the 

 growth of the animal fusion takes place to form the deli- 

 cate framework. The sponge skeleton consists of longi- 

 tudinal and circular silicious strands intersecting in such 

 a way as to form meshes. Besides these there are ridges 

 of fibers which run spirally around the skeleton. The 

 upper end is closed by a sieve-like plate, while at the 

 lower end long silicious spicules extend downward to 

 anchor the animal in the mud. In dried specimens of 

 the skeleton these long, fiber-like spicules are usually bent 

 upward around the base of the sponge, and they are also 

 thus represented in drawings. Such specimens and fig- 

 ures are misleading, since these spicules always extend 

 downward and outward for the purpose of firmly anchor- 

 ing the animal. 



An interesting case of commensalism is offered by 

 Euplectella, since it often harbors within the hollow of its 

 vase-like structure a little shrimp, Spongicola. 



In the Hexactinellida there is no drainage canal sys- 

 tem, as the large ampullaceous sacs open directly into the 

 great cloacal tube which is closed at the opening above 

 by the sieve-like plate. 



The % members of this group resemble the Calcarea in 



