EECEEATIVE SCIENCE. 



Ill 



of the body, and tlius it gets its living. 

 "Within the mass of the creature are the 

 "many stomachs" which form the basis for 

 the • classification of the polygastrica ; bnt 

 they are mere vesicles surrounding a solid 

 nucleus. The vesicles are by no means per- 

 manent ; they appear and disappear according 

 to the -wants of the creature, which thus 

 manufactures arms, legs, and stomachs as it 

 wants them, and resolves them back into its 

 own amorphous jelly-like body as soon as 

 their purpose has been served. Now the 

 physiology of a sponge may be considered to 

 assimilate very closely to that of a rhizopod, 

 for the gelatinous flesh consists of an agglo- 

 meration of separate bodies, each formed 

 on the plan of an Amoeba, yet acting in 

 concert, and subsisting in one harmonious 

 scheme of organization. At 4 is a represen- 

 tation of a part of the body of G-rantia, one 

 of the marine sponges, which is seen to con- 

 sist of a sort of community of Amoeba, with 

 real cilia instead of pseudopodia. We can 

 understand, therefore, how the cUia cause a 

 current of water through the meshes of the 

 sponge, how the particles of nourishment are 

 seized and appropriated by the stomachs, 

 and the rejected matters cast out with the 

 efflux of the stream from the interior. This 

 sponge has no net-work, and in this respect 

 differs from the ordinary type of structure. 



If we again take note of the porous sys- 

 tem, which indeed is that which, to ordinary 

 eyes, is all that is noticeable about sponges, 

 we shall observe that the larger channels are 

 few in number, but the small ones ramify 

 through the whole mass. The larger aper- 

 tures are called " oscula," and the smaller 

 pores and the two sets of apertures are con- 

 nected within by means of canals, which 

 again connect with another set of canals, and 

 thus constitute a true circulatory system 

 from without by the pores to within, and from 

 within to without by the oscula, and to the 

 whole of these the horny, calcareous, or sili- 

 ceous frame-work gives consistence and form. 



The passage of the current through the 

 whole of its course may be very prettily 

 observed under the microscope, by adding to 

 the water in which a living specimen is placed 

 a little finely -powdered indigo. Dr. Grant, 

 in 1827, first revealed to the world this curi- 

 ous passage in the history of the sponges, to 

 which has been added numerous additional 

 details by more recent observers, among 

 whom Mr. Bowerbank stands in the first 

 rank. It should be added, as redeeming 

 the sponge from the very low position in 

 which we place the Amoeba, that it can open 

 and close the oscula at pleasure, and that it 

 has the power of forming new oscula if a 

 larger current be required. These actions 

 have been observed by Mr. Bowerbank in 

 the common fresh-water sponge. 



The story of this wondrous life is not yet 

 complete. The sponge can patch up any por- 

 tion of its tough integuments that may suf- 

 fer damage, and if two separate fragments 

 are brought into juxtaposition, they will 

 probably join together and become one mass 

 as complete as if ah initio united. Professor 

 Huxley has made observations on the inte- 

 resting species called Tethys, which consists 

 of a central whitish granular mass, associated 

 with cylindrical spicula. Around this is a 

 yellowish substance containing ova and stel- - 

 late spicula. External to this is a sort of 

 sheathing substance called the cortical layer, 

 shown of a darker tint on the margin of the 

 section. This cortical layer is of a deep red, 

 deepest towards the margin, and shading off 

 to a lighter zone inwards. The lighter portion 

 consists of closely- woven bundles of fibrous 

 tissue, with here and there in its substance 

 stellate spicules, while the darker outside 

 zone is granular, and contains great numbers 

 of crystalline spheres beset with short conical 

 spikes (8). Throughout the whole substance 

 are bundles of spicula ; at the centre they are 

 somewhat regular in arrangement, but be- 

 come more and more confused as they ap- 

 proach the cortical layer, so as to brace 



