Sponge-fauna of Norway. 145 



tinguish the excurrent and incurrent canals in hops are to be 

 met with here. 



The ultimate excurrent canaliculi flowing from the flagel- 

 lated chambers join together into larger canals; and these, 

 after one or more confluences, empty themselves into one 

 or other of the main excurrent trunks, which, maintaining a 

 tolerably uniform diameter for a considerable part of their 

 course, at length open freely into a large, more or less spheri- 

 cal chamber (PI. VI. flg. 1, C, fig. 2, b) ; this chamber com- 

 municates, through an aperture guarded by a thick muscular 

 sphincter, with a smooth-walled cylindrical tube (fig. 1, T, 

 fig. 2, a), the external opening of which is somewhat reduced 

 by an extension inwards of its surrounding margin. The 

 walls of this tube, as well as its outer rim, consist of vacuo- 

 lated tissue, covered by the epidermis, dermis, and bacillar 

 layer ; the vacuolated tissue extends down to the subcortical 

 layer, which here consists of gelatinous connective tissue of the 

 usual composition (fig. 1, c), bacilli, and long, delicate, 

 thread-like fibres, a little swollen, granular, and nucleated in 

 the middle, and directed lengthwise towards the sphincter ; 

 the free face of the subcortical layer, which here forms the 

 wall of the spherical chamber, is covered by a dense layer of 

 dark grey granular fibres (fig. 1,/'). 



The vacuolated tissue of the outer tube exhibits as it ap- 

 proaches the sphincter an increasingly large admixture of 

 fibres, which appear partly to arise between its cells, partly 

 to be introduced from the globate layer. 



The sphincter is formed by the union of the subcortical 

 tissue with that of the wall of the outer tube. Wiien these two 

 meet they assume a common direction, so as to extend across 

 the axis of the tube ; the tissue of the outer tube forms the 

 upper part of the sphincter, and is traceable as a distinct 

 component almost close up to its centre ; it gives us the 

 distinct small epidermal cells covering the upper surface, the 

 bacilli beneatli, and lower still the vacuolated cells inter- 

 mixed with granular fibres. The subcortical layer forms the 

 lower two thirds of the sphincter ] it furnishes the layer of 

 epithelial cells covering the lower face of the muscle ; its 

 outer dark granular fibrous layer sweeps into the dower part 

 of the sphincter, increasing in thickness as it goes ; while its 

 gelatinous connective tissue constitutes the middle layer of 

 the sphincter, extending into it as an intrusive wedge-like 

 mass. Near the centre of the sphincter all tliese various 

 constituents, except the e])ideruial and ejiithelial hiyers, are 

 represented by dark-grey granular muscle-fibres alone, whicli, 

 taking a concentric, radiating, and vertical direction, form a 



