E. IMPEEIALIS. — GEiV. CHAKACTEKS. 67 



itself penetrates the mud-ball. The sponge thus stands tolerably 

 firmly implanted in the substratum, unlike certain other species 

 (e. g., E. marshalli) in which the body, being rooted by the basal 

 tuft only, apparently admits of being subjected to a free sway- 

 ing motion as it stands on the sea-bottom. 



The buried extremity of the skeletal tube, which is narrowed 

 to about ^5 the diameter of the aieve-plate at the superior end 

 and which is quite dead, is found to be open when cleansed of 

 the mud ; a perforated bottom-plate does not exist. However, 

 in quite young specimens under 75 mm. body-length I have 

 found the inferior end, which probably stands yet unburied in 

 the mud, blindly closed by the living tissues (rtV?e anon). 



Turning our attention to the features of the parietes on the 

 gastral side (PL II, fig. 5), this surface is as usual checkered 

 with tolerable regularity by the transverse aud longitudinal ridges. 

 Much less conspicuous than these are the two systems of the 

 right-handed and the left-handed oblique ridges. All the ridges 

 bear numerous small excurrent apertures, generally not more 

 than Y4 mm. in diameter. jNIany of the meshes too contain 

 each one large or 2-4 smaller pits, which, by holding the wall 

 against light, can at once be recognized as the apertures of large 

 excurrent canals arising in the external parietal ledges. The rest 

 of the meshes are each occupied by a cup-like or pit- like de- 

 pression, the bottom of which is perforated by a parietal osculum. 

 Not uncommonly two or more of these perforated meshes are 

 found in direct succession either transversely or longitudinally. 

 However, their distribution in relation with that of the other 

 kind of the meshes — the so-called interstitial meshes — must be 

 said ou the whole to be irregular. 



