HARDWICKE'S SCIENCE-GOSSIP. 



197 



Their power of locomotion when on land being 

 exceedingly limited (we have never seen one walking), 

 their sociable disposition, such as it is, could hardly 

 be exhibited to any great advantage. On various 

 occasions we have seen numerous oyster-catchers, and 

 even a black-backed gull or two, in the immediate 

 vicinity of a wing-drying band of cormorants ; but 

 we never saw any hostility or discourtesy displayed 

 on either side, each species seeming invariably 

 disposed to mind its own business. Cormorants, 

 moreover, being as regards sight, hearing, build, &c, 

 and every other respect, specially adapted for a sea 

 life, their appearance on shore may be regarded as 

 merely for the purposes of repose and relaxation, and 

 not, as with gulls, ducks, &c, for conjoint and 

 harmonious consumption of shell-fish, &c. 



THE STRUCTURE AND DISTRIBUTION 

 OF SPONGES. 



By the Rev. H.Walter Syen, M.A. Cantab. 



THE nature of sponges, whether animal or 

 vegetable, was long a disputed point with 

 naturalists. But it is now placed beyond dispute 

 that the sponges are really animals, and animals 

 endowed with a very interesting and somewhat 

 complex organisation. The general structure of a 

 sponge is familiar to all, but it must not be supposed 

 that the domestic "sponge" constitutes the whole or 

 the most important portion of the animal. In fact, 

 the part of the sponge which is used in every-day 

 life, is little more than the skeleton forming the 

 foundation of the animal structure. Every one is 

 acquainted with the nature of this skeleton, consisting 

 as it does of homy fibres interlacing and crossing in 

 every direction, and in this manner forming a loose 

 yet tough and strong mass of cells and passages. To 

 this fibrous material the name "keratode " (Kepas, 

 horn ; elSoy, form) has been applied, from its horny 

 nature. The essential portion of the animal consists 

 of a soft, more or less gelatinous substance, con- 

 tained within and supported by this horny framework. 

 This substance pervades all parts of the sponge, and 

 in some cases forms the entire structure ; the horny 

 framework being entirely absent. Both the keratode 

 and sarcode substance (<rap|, flesh ; 686s, way) are 

 generally abundantly provided with calcareous or 

 siliceous spicules, which assume various shapes and 

 sizes. The spicules found in the sarcode are fre- 

 quently radiate or star-shaped, and are hence named 

 "stellate." Closer examination reveals the fact that 

 the sarcode, or sponge-flesh, is not homogeneous. 

 For, on being submitted to the microscope, it is seen 

 that this sarcode is made up by the aggregation of a 

 number of minute bodies, rounded in form and with 

 a general resemblance to an Amoeba. These bodies 

 are the sponge-particles, or sarcoids, and are the 

 ultimate constituents of the animal. Some of them 



are provided with cilia, by which they are enabled to 

 create currents in the surrounding water, the object 

 of which is doubtless to bring food within reach of 

 the animal. These, then, are the three portions of the 

 bodily structure of a sponge — sarcoid matter, keratric 

 or horny framework, and spicules. It should be noticed 

 that the only portion which is invariably present is 

 the flesh-substance, this being the truly essential 

 portion of the animal. In some sponges both kera- 

 tode and spicules are absent. If an ordinary 

 " sponge " be examined, it will be noticed that the 

 surface is provided with a great number of orifices ; 

 and some of these are, comparatively speaking, few in 

 number and project a little from the surface. The 

 remaining orifices are infinitely more numerous and 

 much smaller. To the larger of these orifices the 

 name "oscula" has been given, and to the smaller 

 that of "pores." It is by means of the "oscula" 

 and "pores" combined with the circulatory system 

 connected with them that the constant passage of 

 water through the sponge is effected. For it will be 

 found on careful examination (which may be effected 

 by examining a small portion of living sponge in a 

 glass under the microscope) that currents set in at 

 the pores, traverse the system of canals permeating 

 the sponge, and finally escape through the oscula. It 

 has been mentioned above that some of the sarcode 

 particles are provided with cilia, and it is by the 

 movements of these cilia in the main that the circu- 

 lation is carried on. For it has been ascertained that 

 within the external wall, or dermal membrane (dermis, 

 the skin), there exist a number of chambers, the 

 walls of which are lined with these ciliated particles, 

 and into these chambers the pores open. The reason 

 of this circulation is obvious. By its agency nutri- 

 tious particles are brought from a distance for the use 

 of the sponge, and effete matters are removed. It 

 should also be noticed that this apparatus may like- 

 wise be looked upon as a mode of respiration, 

 presenting us thus early, as it were, with an example 

 of an aerating process in the animal kingdom. It is 

 very possible that each particle of sarcode matter 

 appropriates for itself, and by itself, whatever food 

 may be thus brought in its way, much in the same 

 manner as does the Amoeba. And indeed there seems 

 much consistency in the view which is held by some 

 that in reality the sponge is made up of amcebae, kept 

 together by the fibrous framework, so that each sponge 

 is in reality a colony of amsebse every one of which 

 lives independently of the rest. Be this as it may, the 

 resemblance both in structure and in function between 

 the ultimate sponge-particles and the amoeba?, is at 

 the same time suggestive and striking. The develop- 

 ment of sponges has not been quite satisfactorily 

 worked out as yet. But it has been clearly shown 

 that there are two distinct modes of reproduction. 

 The first is a true sexual process, the second asexual. 

 Examples of the first can be studied in Tethya and in 

 other genera. In these cases it is found that some 



