OCR Text |
Show 1877.] FIVE N E W SPECIES OF SPONGES. 463 with sarcode, which appeared to be in a partially decomposed condition. The skeleton-structure, like that of the spongious base of Hyalonema mirabile, is composed of irregularly dispersed fasciculi of long spicula; but the fasciculi are less compact in their structure, and amid them there are numerous single spicula as irregularly dispersed as the fasciculi are. The form of the skeleton-spicula in the sponge in course of description is very long, slender, cylindrical, with incipiently spinous clavate terminations ; and intermixed with them there are a few very large and stout acuate ones. The best view of the skeleton-structure is to be seen in portions of the sponge from the inner surface of the cup. At this surface the dermal membrane appears to be aspiculous; but immediately beneath it, in the portion examined, there were numerous groups of sexradiate stellate retentive and defensive spicula, densely packed in detached masses of sarcode. This congregation of spicula in separate masses is probably due to the partial decomposition of a uniform stratum of sarcode in the living sponge in which these minute organs abounded. The sexradiate stellate spicula are exceedingly slender, and average TTJVC ^ncn- *n extreme expansion. They appear to vary considerably in the number of their furcating spicula-some radii being trifurcate, while others are bifurcate ; and very few have the full number of the furcating radii. The interstitial spaces of the skeleton are abundantly supplied with cruciform spicula with cylindrical incipiently spinous radii. The normal form of these spicula is evidently rectangulated sexradiate. The greater number of them are cruciform ; but a considerable number have the fifth ray, or basal portion of the shaft; and a few of them are completely sexradiate. There is a very great difference in size between the two sets of spicula-those appropriated to the dermal system with attenuated radii, and the smaller and much more abundant ones of the interstitial spaces with cylindrical radii, the expansion of the radii of the dermal ones averaging -^ inch, while those of the interstitial spaces seldom exceed yi-g- inch in the expansion of the cruciform radii. The minute attenuato-acuate spicula, which are numerously dispersed on the interstitial membranes, average about -%-fc-§ inch in length ; and it appears probable that they are really the radiating spicula broken off from the very numerous sexradiate stellate spicula that are crowded together in such great numbers in the interstitial masses of sarcode. The skeleton-spicula are many of them flexuous ; their average length is •£$ inch, while the diameter of a fully developed one measured only -g-oV-j inch. The loosely arranged fasciculi of the skeleton-structures of this sponge seem to closely ally it to the spongious base of Hyalonema mirabile; while the physiological structure of its expansile dermal system with its quaternate connecting spicula, and, to a considerable extent, its anatomical structure, are in perfect harmony with the corresponding parts of the genera Alcyoncellum, Rossella and Geodia; and the minute rectangulated sexradiate stellate forms of retentive |