REPORT ON THE MONAXONIDA. XXxi 



side of the elongated pore-areas, but are often obliquely placed and often branched. 

 Judging from their relation to the surrounding parts we have little hesitation in pro- 

 nouncing them to be muscular in function. 



Immediately below the dermal membrane thus constituted, we find, except of course 

 where the subdermal cavities are situate, the gelatinous tissue which makes up all the 

 rest of the ectosome. This is very loose indeed, and appears to be composed of a frame- 

 work of stellate cells, each with a very small round nucleus ; amongst which are scattered 

 numerous other cells of a very diiferent kind. These (PI. XL VIII. fig. 2c, c. ) are large, 

 averaging about 0*0 15 mm. in diameter, irregular in outline and usually granular, though 

 not very distinctly so. They stain very deeply with borax-carmine and are especially 

 abundant around the ends of the inhalent canals. It is very diflicult to decide under 

 which of the five heads above mentioned these elements should be classed, pro- 

 bably with the amoeboid cells. Another important constituent in the ectosome of 

 Esperella murrayi is furnished by very numerous, irregularly scattered trichodragmata 

 (PI. XLVIII. fig. 2c, t) ; it seems very probable that in this and similar cases the tricho- 

 dragmata, like straw in mortar, serve to bind together the loose, gelatinous tissue in 

 which they lie. 



In Esperella lapidiformis we have found, embedded in the gelatinous ectosome, 

 numerous very young ova, each consisting of a rounded, granular cell, commonly about 

 0"02 mm. in diameter, with a small, but very distinct, central nucleus; while in the 

 deeper parts of the sponge (choanosome) there are numerous developing embryos as 

 well as young ova. 



When, instead of being gelatinous, the ectosome is firm and tough, and contains a 

 large proportion of fibrous tissue, we have a true cortex, such as may be studied to the 

 best advantage in the Suberitidse. Although the general direction of the fibres is usually 

 more or less parallel with the surface, we commonly find also bands of fibrous tissue 

 irregularly surrounding the subdermal cavities, as, for example, in Stylocordyla 

 stipitata, var. glohosa (PI. L. fig. la, f.t), and Suheintes perfectus (PI. L. fig. 2, f.t). 

 In Suherites perfectus also, as we have already noted, the fibrous tissue dips into the 

 choanosome and ensheaths the skeleton-fibres. 



In Tentorium semisuberites (PI. L. figs. 3, 3a) the ectosome on the upper surface of 

 the sponge is more than usually fibrous and is divisible into three distinct layers. There 

 is (1) an external layer (PL L. fig. 3a, a) about 0'05 mm. thick, wherein the fibres are 

 mostly placed parallel with the surface ; (2) a much thicker, but less dense, intermediate 

 layer (PI. L. fig. 3a, h), which is honeycombed by the very numerous, elongated sub- 

 dermal cavities (s.c), and in which the fibres are mainly placed vertically to the surface ; 

 and (3) a dense internal layer (PL L. fig. 3a, c), rather thicker than the external layer 

 and, like it, with the fibres mostly arranged parallel to the surface. We know that this 

 species has a remarkable power of contraction, which chiefly afi"ects the upper, pore- 



