7 66 PORIFERA. 



and the back stroke being made with the edge, so as to meet with the least possible 

 resistance. 



If the reader will refer to the figure of the VORTICELLA, he will find that the footstalks 

 on which the bell-like cup is seated are of considerable length, and capable of being 

 shortened by being coiled into a spiral form. This is by no means an uncommon Inf uso- 

 rian, and is very liberal in displaying this capability. It is usually found associating in 

 groups, so that there is hardly a stage in its life of which some example cannot be dis- 

 covered. Though devoid of apparent organs of sense, this creature is marvellously 

 timid, shrinking in a moment if the water be shaken, and tightening its coils until they 

 resemble the spiral rings of a vine's tendril. It soon, however, recovers itself, and by 

 slow degrees permits the spires to uncoil, and waves its fringed head boldly in the narrow 

 prison to which it has been consigned. Sometimes the Vorticella breaks away from its 

 footstalks, and is then carried rapidly through the water by the action of its ever-waving 

 fringe of cilia. 



As is the case with many of its kindred, the Vorticella is able to increase its numbers 

 by the simple process of splitting itself into two distinct beings, each of which is after- 

 wards a 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 subdivision, and forms one of the links that bind animals of a higher 

 type of organization with these lowly, but more 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 futher subdivision, four lads of fifteen. 



THE second figure 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 practiced observer. Some- 

 times 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. Sometimes, as in the Stentor, the Infu- 

 soria 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. 



WE 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. 



