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 Periphragella, 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, — Class 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 



