GLASSY GROUP. 
539 
minutely serrated on the upper edge, and thereby offering resistance to the uproot¬ 
ing of the tuft from the mud. The length of specimens varies from 20 to 30 
inches. 
The Japanese species is obtained from off Tokyo, from a depth of three hundred 
and forty-five fathoms, and is fished for with long lines, weighted and provided with 
hooks, which are dragged along the bottom. Eighteen species have been obtained 
from the Atlantic, Pacific, and Southern Oceans, from depths ranging from a few 
hundred up to two thousand five hundred and fifty fathoms. The allied Semperella, 
shown in the right-hand illustration of the coloured Plate, occurs in one hundred 
fathoms off* the Philippines. It forms a subcylindrical stock, about 12 inches in 
length and 2 inches thick, terminating in a dense tuft about 3 inches long. The 
lace-like skin covers a complicated labyrinth of tubes. Another Philippine form 
(Polylophus ), represented in the bottom right-hand corner of the same Plate, has 
small thick-walled hemispherical cups, with tufts of spicules growing from conical 
projections on the walls, and passing down to form root-tufts. This sponge is 
remarkable for producing buds, which become detached and develop into complete 
sponges. In the middle of the lower part of the Plate is shown a species of another 
genus, known as Periphrcigella, from Japan, which forms a curved funnel, on the 
outer wall of which is a network of tubes which have branched off from the main 
body. In Farrea, seen in the left-hand bottom corner of the Plate, the body is 
formed of forking branched glassy tubes, the walls of which consist of spicules 
whose rays have fused into a rigid framework. Sclerothamnus, from three 
hundred and sixty fathoms off Timor, is a remarkable Dictyonine sponge, which 
forms a bush two or three feet in height, with the branches marked with a spiral 
band. 
Another beautiful type is Carpenter’s glass-sponge ( Pheronema ), shown in the 
illustration on p. 530, which consists of a thick-walled cup, narrowed at the orifice, 
and giving origin below to a thick root-tuft of spicules; the first specimens were 
dredged from a depth of five hundred and thirty fathoms off the Faroe Islands. 
Glass-sponges, with one or two exceptions, have been obtained in deep water, 
from ninety to two thousand nine hundred fathoms. Previous to the deep-sea 
dredging expeditions, specimens had been found in only a few localities, and the 
procuring of them had been due more or less to accident. Thus the Japanese 
fishermen, while in quest of deep-sea fish, brought up glass-ropes, which became 
marketable commodities. Similarly, the Malays found it would pay to explore 
for submarine treasure, and constructed their bamboo dredge. 
Fossil Hexactinellida are found abundantly in the Chalk. The Ventriculites, 
found in Chalk flints, are the skeletons or casts of glass-sponges. 
The Common Sponges,—C lass Demospongia. 
The common sponges include all those which do not come under the designation 
of calcareous or glass-sponges. A negative definition is unsatisfactory, but it is 
difficult to frame a positive one which will apply to all divisions of this class. 
Most common sponges are siliceous, while such as are horny are probably derived 
from siliceous types. They are divided into four orders. In the first or four-rayed 
