132 • Transactions of the Society. 



tracery of secondary fibres, when it closely resembles the (Plate 

 VIII., Fig. 5) dermal layer of some fossil sponges. The chief fibres 

 of the basal layer are formed on a framework of sexradiate spicules, 

 which may be revealed as casts by boiling in caustic potash ; the 

 secondary fibres appear to originate in threads of silicifying 

 sarcode, which have crossed from one side of a mesh to the other. 

 These secondary fibres must not be confused with the secondary 

 fibres of the body skeleton ; the latter spin across large meshes, 

 and are moulded on spicules, the former across meshes of the small 

 fibre, and are not deposited on spicules. 



The oscules of the inner surface of the sponge exhibit a tendency 

 to elongate into channel-like grooves, following a radiate direction 

 with respect to the axis of the vase, and soaiewhat resembling the 

 grooves of the under surface, though of much smaller dimensions, 

 never exceeding, for instance, an inch and a half in length. 



The openings of the upper surface are so abundantly spined by 

 prolongations of the body skeleton as to give to the whole interior 

 of the cup a rough spinose appearance, which is in marked contrast 

 to the smooth, even surface of tlie unspined fibres of the under side. 

 In Fig. 2, Plate V., the spines produce round the oscules the appear- 

 ance of a denticulated mai-gin. They may be obtained readily for 

 microscopic examination by breaking off with a fine-pointed pair of 

 scissors, and catching them as they fall on a spread-out sheet of 

 glazed black paper. Three such spines are represented in Figs. 2, 

 3, 4, Plate VI. They consist of a prolongation of the skeletal net- 

 work into a generally hollow reticulate and pyramidal spine, which 

 might be very appropriately named a "lantern-spine" from its 

 rough resemblance to the lanterns used in architecture. The longi- 

 tudinal fibres of the spine usually become much thicker with age 

 than the rest, as may be seen in Fig. 2, where they have entirely 

 obscured the transverse fibres from sight, if transverse fibres ever 

 existed. The subsequent deposit of silica has, indeed, in many cases 

 so thickened the fibres and modified the original reticulate form as 

 to lead one to doubt whether they were ever modelled on a sex- 

 radiate form. A little boiling in caustic potash, however, will soon 

 reveal the imbedded sexradiate spicules, which possess here just 

 the same characters as in other parts of the network. The deposit 

 of silica over them is so thiciv, however, as to overwhelm them 

 altogether in some cases, as, for instance, in the lateral secondary 

 spine (Fig. 3) projecting from a principal one, which is not repre- 

 sented in the figure, but the direction of which is indicated by an 

 arrow : in this instance we have a conical spine moulded over a 

 sexradiate spicule, and the same thing has taken place in the 

 pointed end of a spine shown at Fig. 4. The spines frequently 

 support one or more long acerate spicules, which pass through 

 and project beyond them like a lance in rest. Now and then these 



