200 PLATE Lxxiir, 



determined with precision, but there is every appear- 

 ance that they have been small and simple in their 

 structure. The skeleton structure in the interior of 

 the sponge is quite as large and coarse as it is at the 

 surface. The spicula forming the fibre are large and 

 stout, and nearly all are more or less flecto-acerate. 

 The areas of the network of the skeleton are large and 

 irregular in form, and single skeleton spicula are fre- 

 quently projected into their spaces as internal defensive 

 spicula, at right angles to the fibres forming their 

 parieties. The external defensive spicula are also 

 projected from the surface-fibres in like manner, and 

 the minute hispidation of the surface is not visible to 

 the unassisted eye, but in sections at right angles to 

 the dermis when mounted in Canada balsam they are 

 very distinctly demonstrated. The interstitial mem- 

 branes are very delicate in their structure. They are 

 abundantly supphed with the same forms of spicula 

 that are found in the dermal membrane. The dehcately 

 slender tension spicula are not so numerous as the 

 anchorate ones. The latter forms are especially charac- 

 teristic of the species ; they are exceedingly minute, 

 being barely visible when separated from the sarcode 

 by boiling in nitric acid, by a hnear power of 200, but 

 to define them in a satisfactory manner they require a 

 power of about 700 linear. Although so minute, they 

 are fully and completely developed. A large-sized 

 palmato-anchorate one measured ^^qq inch in length, 

 and one of the bidentate equianchorate ones twTs iiich 

 in length. Their length very slightly exceeding the 

 diameter of a skeleton spiculum, the latter being 

 rrto inch. 



The tricurvato-acerate, tension spicula are also very 

 characteristic of the species; they are very long and 

 slender, and are not readily to be detected amid the 

 tissues. The angular flexure in the middle of the 

 shaft varies considerably in its form, and occasionally 

 it assumes that of a loop. The shaft from the middle 

 to either extremity is usually very nearly straight. 



