Sponge-fauna of Norway. 251 



transparent, narrow trabecule, enclosing clear transparent 

 cavities, each of which is provided with a round nucleus and 

 nucleolus lying on the side of one of the trabecules (PL XL I. 

 fig. 24). This is its character in its most completely special- 

 ized state ; when less specialized its constituent cells can be 

 easily made out (PL XII. fig, 25, a to e). They are 0-001 

 inch in diameter, of a round, oval, or irregularly polygonal 

 form, and consist of an outer thick hyaline thread-like border 

 or cell-wall, enclosing a large clear vacuole, and a small 

 quantity of finely granular colourless sarcode, in which is im- 

 bedded a round nucleus with its nucleolus. They appear to 

 be produced by the metamorphosis of the ordinary protoplas- 

 mic cells of the mark, and, by the fusion of their outer borders 

 where these touch one another, give rise to the parenchyma- 

 like tissue just described, to which the name of " vacuo- 

 lated connective tissue " may be applied. The layer which 

 this tissue forms beneath the epidermis is of variable thickness, 

 on an average from 0'002 to - 003 inch ; it is distinguished 

 by the entire absence of cylindro-stellate or other spicules, 

 the only spicules which occur in it being the small fusiform 

 acerates, which penetrate at one end the subjacent globate 

 layer, and project at the other beyond the surface of the sponge. 

 It may be as well to give this layer of tissue a distinct name ; 

 and though the term " dermis " is not altogether free from 

 objection in its application here, it has, at least, the merit of 

 convenience. 



The next layer of the cortex, 0"01 inch thick, is that of the 

 globate spicules (PL XI. fig. 7, c). The characters of these 

 have most of them been already described by other observers. 

 It is a fact, however, worthy of special mention, that some of 

 these spicules contain within a well-marked pit-like hilum a 

 distinct oval nucleus with a spherical nucleolus. 



The globates do not lie loosely aggregated together, but 

 are regularly conjoined by short thick fibri Hated ligaments. 

 The ligaments pass directly from the side of one globate to 

 the opposed face of its nearest neighbour ; and since in the 

 plane of a single transverse section one globate may be seen 

 surrounded by five or six others, so there will also be seen 

 five or six ligaments proceeding from it, like the spokes of a 

 wheel, one for each of its surrounding fellows. As the sur- 

 rounding globates are also joined to each other by ligaments, 

 so a number of triangles are produced, having the ligaments 

 for their sides and a globate lying on each angle. The centre 

 of the triangle, which is left vacant by the ligaments, is occu- 

 pied by a cell or cells, which, with their nuclei and nucleoli, 

 exactly resemble one of the vacuolated cells of the dermal 



