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Show 1875.] SPECIOSUM AND HYALONEMA MIRABILE. 609 adds considerably to its strength ; and the membranes of the areas are abundantly supplied with the minute quadrihamate defensive spicula, which are all disposed on the membrane on their flat surfaces. In the structure of the upper portion of the dermal membrane the rete is open and diffuse, and the areas assume an irregular elongate form ; and the rete is composed only of large inflato-acerate spicula, without apparently any intermixture of the large rectangulate sexradiate ones, which are of such common occurrence in the basal portion of the membrane. Another distinctive structural difference is, that the areas in the rete of the dermal membrane are furnished in a strikingly beautiful manner with the spinulate cruciform defensive spicula, which are abundantly disposed on all parts of the surface at nearly equal distances from each other in a manner closely approaching regularity ; and nearly all of them are projected at right angles to the surface on which they are based. The minute quadrihamate spicula so abundant on the basal membrane are very rarely to be detected on the upper dermal one. These structural modifications of the dermal membrane indicate the difference in the respective offices of tbe two parts of the animal in a very striking manner ; but not to a greater extent than we may observe in many sessile British sponges under similar circumstances. A minute description of these characters of the respective parts of the dermis of the sponge are especially necessary, as much misapprehension has existed in the minds of some naturalists as to the true position of Hyalonema in its natural locality, some having imagined that the pointed end was deeply plunged into the bottom of the sea, and that the sponge-mass was the distal termination of the animal. In all sponges with which I am acquainted, the attachments are either adhesive, or clasping like the roots of Fuci, never penetrative like the roots of plants that derive nutriment from the soil, which sponges never do. The idea of the slender pointed distal termination of Hyalonema being plunged into the sea-bottom, and thus supporting a heavy mass of sponge at its opposite end, is contrary to all we really know of the usual habits of these animals in their natural localities. In corroboration of this opinion, I may state that amongst the various specimens of this species of sponge which I possess, I have one thirteen inches in length, the distal extremity of which for six inches of its length is completely enveloped by the corium, which has the usual mamilloid organs upon it up to the extreme apical termination. These organs, which have been supposed to be polyp-cells, would have been in a very strange position had they ever been immersed in the soft substance of the sea-bottom. In further elucidation of this subject, I may refer m y readers to an article on Hyalonema in 'Land and Water,' for February 13, 1871, p. 219, written, I am informed, by a naval officer of the name of Templar. He writes:-"For Dr. Bowerbank's theory concerning Hyalonema, ' or the long glass-rope sponge,' and his belief in the siliceous spicula growing upwards, the sponge adhering to a rock, I have great respect as well as belief. His friend, Mr. Henry Lee, wrote to me when in Japan to try and discover 'if such was the case;' and from what I |
