156 



CLASS-SPONGIA. 



CLASS XVI. SPONGIA. 



NOTWITHSTANDING the various inquiries which have been made in regard to the Class of Sponges, but little is known as to their true 

 nature, beyond the anastomosing horny filaments of which their framework consists, and which, whilst the Sponge remains alive 

 in water, is overspread with a thin layer of glairy semifluid matter. In many instances, the elasticity observed in the Common 

 Sponge does not exist, an unyieldingness being imparted to the mass by the deposition in its interior of crystallized spicuk of 

 various form, consisting of calcareous or siliceous matter, corresponding in shape to the raphides observed in vegetable structures, 

 and which exhibit determinate forms in different species. The whole surface of the Sponge is studded with innumerable and 

 minute apertures which lead to canals in its interior, and these, gradually coalescing and forming larger and larger passages, ter- 

 minate in cavities which open by large and commonly projecting orifices upon the surface of the Sponge. Through the minute 

 orifices the water is absorbed into the Sponge, and is poured out of it in continuous streams by the large apertures. Locomotion 

 does not belong to the Sponges ; they are permanently fixed, excepting at their first production, when, according to Dr. Grant's 

 statement, the gemmules from which they are generated are furnished with cilia, and capable of moving about in the water till 

 they have selected a spot, where they attach themselves and remain throughout the rest of their existence. 



LAMARCK has described one hundred and thirty-eight species of Sponges, 

 to which the editors of the last edition of his great work, Histaire Naturelk 

 des Animaux sans Vertebres, have added nine ; these he divides into seven 

 sections : 1st. Sessile masses simple or lobed, forming either coverings or 

 inclosures; 2nd. Subpediculate masses, or those contracted at their base, 

 simple or lobed ; 3rd. Pediculate masses, flattened or fan-shaped, simple 

 or lobed ; 4th. Concave expanded, cup-shaped or funnel-shaped masses ; 

 5th. Tubular or pipe-shaped masses, not expanded ; 6th. Foliaceous masses 

 or divided into flattened lobes, leaf-shaped ; and 7th. Branching, shrub or 

 tree-like masses. Of these, however, some certainly are plants; and from 

 the observations of Dr. Grant it is perfectly clear that among the others the 

 types of 'three distinct genera are to be found, although it has not been 

 hitherto possible to distribute the whole into their proper places, on account 

 of the difficulty, and, in many instances, the impossibility, of obtaining the 

 species in a recent state, in which only can its true structure be properly 

 examined. 



Whilst alive, the fibres of which the skeleton (as it may be called) of 

 the Sponge consists, are everywhere covered with a transparent, soft, and even 

 glutinous matter, which also spreads over the external surface, and lines the 

 cavities, penetrating from the pores and fecal orifices into the interior, and it 

 is in this soft matter that Lamarck considers the polyps of the Sponge reside, 

 the existence of which, however, has not hitherto been ascertained. 



It is to Dr. Grant we are indebted for a knowledge of the fact, that the 

 fibres of which the skeleton consists are composed of three diflferent kinds 

 of materials, or rather, that of the three groups which he has at present 

 discovered in Lamarck's genus Spongia, each group exhibits a difference of 



structure and material in the composition of its skeleton, and hence he has 

 divided them into the genera Sponges, Calcareous Sponges, and Siliceous 

 Sponges, or, as they are called by Blainville, who retains the old generic 

 name for the first, Spongia, Caldspongia, and Hcdispongia. 



The species already determined to belong to this genus, as denned by 

 Dr. Grant, are distinguished by a skeleton or axis, consisting of cylindrical, 

 tubular, horny fibres, dissolving without efferves- 

 cence in acids, leaving no trace when rubbed on 

 glass, and, like burnt hair, emitting a horny 

 odour : when examined beneath a microscope, 

 they are shown as nearly of the same size, smooth 

 externally, translucent, and of a brownish-yellow 

 colour; tough, flexible, very elastic, generally .-ponge. 



quite straight, and anastomosing freely with each other. Their diameter 

 is about a third of that of a human hair, one-half of which is occupied by 

 their internal cavity, and they unite at a distance varying from one-tenth 

 to a whole line, at all angles, dilating into small angular cavities, where 

 they meet, and communicating freely with each other, so as to form one 

 shut cavity throughout the whole Sponge, which, as they wind around the 

 canals and pores, cannot therefore be the cells of any polyps or other 

 animals causing the currents already mentioned. This part, the axis or 

 skeleton, is that which is employed in commerce, or preserved in collections. 

 But between all the fibres, when the Sponge is alive, there is another 

 substance, soft and transparent, which readily putrifies and washes away 

 after death, and it is probable that in it, if any where, is placed the resi- 

 dence of the animals by which the Sponge is formed. 



anil Snake. 



