POEIFERA. 



587 



complete and perfect being. At first, a single notch is seen upon the edge of the lip, but as 

 time passes on the notch deepens, the cleft becomes more apparent, and in a wonderfully short 

 space each half of the Vorticella is changed into a perfect individual, which in its turn is 

 ready to divide and subdivide itself ad infinitum. It is a truly strange process, this sub- 

 division, and forms one of the links that bind animals of a higher type of organization with 

 these lowly, but not imperfect beings. Thus, therefore, the Vorticella never need die of old 

 age, for it renews its youth, as it were, by this voluntary division, just as if a man of sixty 

 were to split himself down his spine, and thus become two young men of thirty, or, by further 

 subdivision, four lads of fifteen. 



The figure in the illustration represents the Stentor, so called because its general shape 

 bears some resemblance to that of a speaking-trumpet. This is a comparatively large species, 

 being visible to the naked eye, and readily distinguished by a practised observer. Sometimes 

 it is found singly, either attached by its base or swimming boldly through the water ; but in 

 most instances it gathers itself round duck-weed, or floating sticks, and is produced in such 

 numbers that its vast multitudes quite resemble a fringe of soft, filmy slime. 



Like the preceding animal, the Stentor multiplies by self -division ; but it is very likely 

 that many other methods of increasing its numbers are employed. There is, for example, in 

 these creatures, the remarkable phenomenon called "conjugation," which is almost identical 

 with the same act as performed by some of the microscopic vegetables. If two free Infusoria 

 of the. same species — say, for example, the common Paramecium, that swarms so largely in 

 stagnant waters — happen to meet at the proper season of the year, they adhere firmly to each 

 other, as if they were magnets and iron, and go spinning about the water with no less speed 

 than when each urged its single course. A vast number of very minute eggs are then produced 

 by both of the individuals, but the further development of these eggs is not yet known. Some- 

 times, as in the Stentor, the Infusoria are fixed by their bases, and in such instances they bend 

 their mouths towards each other, and so contrive to unite themselves in pairs. 



PORIFERA. 



E now arrive at a large class of beings, which, if they really do belong to the 

 animal kingdom, and are not to be ranked among vegetables, are by common 

 consent allowed to form the very lowest link in the animal chain. 



The name Porifera is given to them because the whole of their surface is 

 pierced with holes of various dimensions, the greater number being extremely 

 minute, while others are of considerable dimensions. The well-known Turkey 

 Sponge, so useful for the toilet, will afford a good example of the porous structure. 

 Yet no one can form an adequate idea of the living Sponge from the dry, dead skeleton 

 which is sold under that name. Many of the species are decked with delicate colors, while all 

 are truly beautiful creatures when viewed in full life and action. They are to be found widely 

 distributed through the seas, and there is hardly a solid body on which a Sponge will not grow. 

 Sponges are generally found hanging from the under sides of projecting rocks at some distance 

 below the surface of the sea, or clinging to the roofs of submarine caverns. Some, however, 

 are strong, sturdy, and branched, and stand boldly erect like the earth-plants which they so 

 wonderfully resemble. 



Even the living inhabitants of the sea are liable to become the resting-places of many a 

 Sponge, and the Crustacea are often forced to bear on their shells the additional burden of 

 living Sponges and other zoophytes much more massive than their whole body. 



