QUEKETT MICROSCOPICAL CLUB. 193 



the chair, and proceeded to give a short address on the spicular 

 structure of a sponge, Geodia japonica, of which he exhibited a 

 dried specimen. His description was illustrated with sketches 

 on the blackboard of the various forms of spicules, with a tabular 

 list of their names. He said that on a former occasion he had 

 brought before the meeting a very different example. He 

 had then purposely chosen a very simple sponge — Dercitopsis ; 

 in the present case a much more advanced condition of the 

 skeleton was found. The general structure of the skeleton 

 in the genus Geodia is figured in Bowerbank's Monograph of the 

 British Spongiadae. Typical specimens of Geodia japonica are 

 cup-shaped ; but they are often irregular in form, and in the 

 specimen shown the cup-shape is not fully realised. It was 

 not intended to give a description of the soft tissues, which it 

 would be impossible to investigate satisfactorily in the dried 

 specimen. There are the usual inhalent pores and exhalent 

 oscula, but in this species these are covered over, and are not 

 conspicuous. In Dercitopsis there is no striking differentiation 

 into what used to be called skeleton and flesh spicules, now 

 known as megascleres and microscleres ; but in all the higher 

 members of the Tetraxonid sponges the difference is very marked. 

 The skeleton spicules are large, and of them the skeleton is 

 built up, while the flesh spicules are small, often very minute, 

 requiring high powers of the microscope to resolve them satis- 

 factorily. It is a curious thing that they are usually scattered 

 between the skeleton spicules, and seem to serve no important 

 purpose in the economy of the sponge. The types of spicules 

 do not differ much in the various species of Geodia. In G. 

 japonica, amongst the megascleres we have first a form belonging 

 to the triaene series, the orthotriaene ; this has one ray very 

 much elongated and three much shorter ones. The short rays 

 lie more or less at right angles to the long ones ; hence the name. 

 The second type is the anatriaene, in which the three short 

 rays curve backwards, making a grapnel form. The third type 

 is very frequent, and is called the oxeote, and consists of a long 

 shaft sharply pointed at each end ; it is sometimes as much 

 as 2 mm. long. The fourth kind of megasclere is a small oxeote. 

 Amongst the microscleres the first type is known as the oxyaster ; 

 it is a star with a variable number of rays, often five or six. 

 These are sharp-pointed and rather long : they are supposed 



