12 



BA RD WICKE'S SCIENCE- G OSSIP. 



microscope, with a few slips and cover glasses, 'are all 

 that is required for the first examination. With their 

 aid the following description can be easily followed. 

 The surface of Ilalichondria panicca is smooth, 

 rising into low elevations, which are surmounted by 

 crater-like openings. If the specimen be examined 

 while quite fresh and healthy, the existence of strong 

 currents streaming out of these openings or " oscula " 

 may be readily demonstrated as follows — take a little 

 carmine or Indian ink and rub it up with sea-water. 

 Now, by means of a glass tube drawn out at one end, 

 that is a pipette, place a little of the water with its 

 suspended particles in the neighbourhood of an 

 osculum, when the upstreaming current will bear it 

 with it. Some of the particles will be drawn to the 

 general surface of the sponge, and the finer ones 

 penetrating by means of microscopical apertures or 

 "pores," which occur in immense numbers, cause a 

 distinct coloration, red or black, as the case may be, 

 which will not wash off. Two opposite currents are 

 thus shown to exist — one passing into the sponge by 

 a great number of finely-divided streams, the inhalent 

 currents, and another passing out of the sponge in 

 comparatively few strong currents, by the oscula. 

 This continual circulation of water through the animal 

 serves to bring food, to carry out effete products, and 

 for respiration. How it is maintained will be seen later. 

 Now examine the surface of the sponge with a 

 lens — it will readily be seen to consist of a thin 

 membrane, the "dermal membrane," supported by 

 a reticulum of spicules. A thin flake of dermal 

 membrane may be sliced off with the point of a razor, 

 or sharp scalpel. A double-edged lancet however 

 best serves the purpose — it is merely pushed under 

 point first. After flattening it out beneath a cover- 

 slip, examine with a low power ; the reticulum of 

 spicules will now appear as a network of interlacing 

 bundles of spicules. These are imbedded in a 

 gelatinous substance, which is the sponge-flesh, and 

 lie more or less parallel to the surface of the animal ; 

 the spicules of the rest of the sponge are also gathered 

 into interlacing bundles, but lie in all planes. The 

 dermal membrane in this form is thus a very definite 

 part of the sponge, with a higher power, J-inch 

 ob. for instance ; careful focussing should enable one 

 to determine the shape of the individual spicule. 

 Each will be found to have the form of a delicate, 

 elongated, double-pointed rod. This rod is rounded 

 in section, and its sides are more or less parallel 

 throughout the greater part of their extent. It may 

 be straight or slightly curved. These points should 

 be accurately noted, since they serve in part to fix the 

 species of the specimen under examination. Such 

 a preparation however, in which the spicules are 

 gathered in bundles and imbedded in a matrix, is not 

 calculated to demonstrate spicular form with any 

 great degree of accuracy. This is best done by 

 completely isolating the spicules ; and since they are 

 composed of silica, and therefore highly resistant to 



the action of reagents, it is easily accomplished. 

 The sponge-flesh may be macerated in dilute hydro- 

 chloric, sulphuric, or nitric acids, or dilute caustic 

 potash. Perhaps the first-mentioned is best ; which- 

 ever is used, the method of procedure is the same. 

 Small pieces of the sponge are cut off and treated for 

 some time with the reagent — on a water-bath if 

 available — the sponge is completely disintegrated and 

 the spicules form a sediment. The supernatant 

 liquid may now be poured off, and the vessel (a test- 

 tube for instance) filled up with water ; after allowing 

 to settle, this is also poured off, and the residue 

 collected on a filter paper on which it is dried — a 

 powdery mass of spicules resulting. A little of this 

 may now be mounted in Canada balsam. Neither 

 glycerine nor glycerine jelly should be used as 

 mounting media, since they may be of the same 

 refractive index as the spicules, which would then 

 totally disappear. All the spicules of Halichondria 

 panicca are of the same form — this is seldom the case. 



Returning to the slice of dermal membrane, a 

 i-inch ob. will show that the sponge-flesh does not 

 form a continuous film. It is pierced at frequent 

 intervals by round openings. These are the fine 

 "pores" mentioned above, through which the 

 inhalent currents stream. 



A slice of dermal membrane should be lightly 

 stained with picro-carmine, and mounted in Canada 

 balsam to form a second reference specimen — the 

 isolated spicules being the first. 



The character of the skeleton other than that which 

 supports the dermal membrane may be demonstrated 

 by a hand-cut section at right angles to the general 

 surface. The section can be mounted in Canada 

 balsam unstained, and also examined in sea-water. 

 By its aid it will be seen that the spicules are of the 

 same form throughout, and that they are gathered 

 into bundles which interlace to form an irregular 

 network ; that is to say, the network is of such a 

 character that no strong structural lines are present; 

 its strands are of much the same thickness throughout, 

 and run irregularly in every plane. This is a dis- 

 tinctive feature. 



We now have a fairly complete knowledge of the 

 skeleton, dermal membrane, pores and oscula. It 

 remains to follow the currents in their passage through 

 the sponge, and to consider the histological structure. 

 The pocket-lens and scaljjel will demonstrate two 

 facts, that the oscula are the orifices of large tubes 

 into which open smaller canals, the lumen of the 

 larger tube being eventually completely lost in the 

 smaller ones ; and that, beneath the dermal membrane, 

 spaces exist into which the pores open. The oscula 

 are one end of a series of internal canals and spaces 

 of which the pores are the other termination. 

 Through the multitude of pores the inhalent current 

 pass, enter a number of delicate canals, and after 

 traversing certain spaces which are enlargements of 

 the lumen of the canals enter a series of larger canals. 



