THE SPONGES. 159 



branching will be found to have taken place in this plane and to one side 

 of it, but scarcely at all toward the opposite side. The colony thus, when 

 viewed from above, presents roughly a semicircular outline, and when 

 viewed from the side, presents one flattened face, which is the face shown 

 in the figure. 



The growth is of such a character that a branch tends to produce several 

 upright terminals, one after another, approximately in the same plane. 

 This is much more marked in the case of some branches than in others. 

 Where it is marked the partial fusion of the terminal branches over their 

 lateral faces results in the formation of imperfect, vertical lamellae, which, 

 however, are only indistinctly developed as such. The terminal branches 

 are cylindrical, rounded at the free end, where there is a depression occu- 

 pied in a few cases by an open, circular osculum, but in general by an 

 oscular membrane, which in the present condition of the sponge is imper- 

 forate. When tlie osculum is widely open, it occupies the whole of the 

 depression, and is 2 mm. in diameter. The oscular membranes doubtless 

 represent closed oscula. 



The terminal branches are about 5 mm. in diameter, and for the most 

 part 15 to 20 mm. high. Their axial (paragastric) cavities, opening above 

 by the terminal oscula, are continuous below with one another and with the 

 axial cavity traversing the rest of the colony. This cavity throughout 

 the colony has a fairly uniform diameter close to 1.5 mm. The wall of 

 the colony is about 2 mm. thick, in some of the terminal branches thinning 

 down to 1.5 mm. 



Color, a very light yellowish brown inclining to ashy. The sponge is 

 tough, firm, and in some measure compressible, flexible, and elastic. The 

 surface is covered with the projecting tufts of spicules belonging to the 

 radial spiculo-fibres. These are just perceptible with a lens, barely so to 

 the touch. 



The pores in general are closed, but in places are open. The}' are in 

 such regions scattered abundantly and without regularity of arrangement 

 over the dermal membrane between the projecting tufts of spicules, and 

 measure 50 to 80 [x in diameter. The pores open into subderinal chambers 

 which in large number underlie the dermal membrane. The subdermal 

 chambers, when seen from the surface, present a lobulated appearance, 

 owing to the fact that they consist of several spheroidal subdivisions freely 

 connecting and often so arranged that the chamber itself is considerably 



