PORIFERA. 
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 charged 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 Stexto r, 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. 
