This view, however, seems scarcely recon cilable with the fact that the motion of the cilia continues in parts separated from their connexion with the rest of the body, portions so small that not more than two or three cilia are attached to them,_ and in which the ope ration of the supposed undulating tubes can scarcely be conceived.
Ehrenberg states that in the Infusoria he observed that the cilia were bulbous at the' root, and that they were moved by small mus cles attached to the bulb. Purkinje and Va lentin also admit the existence of a bulb, and they conceive it likely that the cilia are moved either by muscular substance placed within the bulb, or by certain fibres which they be lieve they have discovered in the adjacent tissue. They describe these fibres as existing in the substance of the membranes or other parts supporting the cilia, being situated at the surface, straight and parallel, and ap-, pearing to be connected together by delicate cellular tissue ; and they think it highly pro bable that they are of a muscular nature.
The whole phenomena of the ciliary motion seem to me most consistent with the notion that it is produced by muscular action. I must confess, however, that I have never seen the muscular fibres described, nor the bulbs.; and perhaps the cilia are not moved merely by muscular fibres attached to their base, like the whiskers of the seal and cat, but may con tain muscular substance throughout a greater or less portion of their length, by which. they can be bent and extended; or perhaps they may in some instances be bent by muscUlar fibres, and resume their original shape and. position by virtue of their elasticity.
We need. not hesitate to admit that 'the. ciliary motion is the result of muscular action' on account of the smallness of the muscular apparatus necessary ; for the researches of Ehrenberg on the Infusoria have brought to light examples of complex organization on as minute a scale as any here required. .Nor need we hesitate on account of the great ra -pidity of action; for there are familiar instance's of muscular motions of equal velocity. The. continuance of the ciliary motion after death and in parts detached from the rest of. the body, and its regularity in these circumstanCei, are appearances, startling at first, but which, though they differ in degree, may be fairly compared with those produced in similar cir-, cumstances by involuntary muscular action, and . may be attributed to the same cause..
Thus the different parts of the heart, which during life contract in a certain order. inde,-. pendently of the will, continne to act m the, same regular order for a time, and in some animals for a long time, after death or sepa ration from the body; and it is remarkable, although perhaps we are not warranted by ob servation to lay it down as a general rule, that there is a correspondence in the duration of the ciliary motion after death and the persistence of muscular irritability. In the Tortoise, for instance, in which it is well known that the irri tability of the heart and other muscles endures remarkably long after death, the ciliary motion is also of extremely long continuance ; while 2D Mammalia and Birds, the ciliary motion and muscular irritability are both comparatively soon extinguished.
On the whole, therefore, without laying any stress on the alleged discovery of a muscular apparatus by Ehrenberg and the other authors mentioned, we may venture to conclude that the facts known respecting the motion of the cilia are all reconcilable with the opinion that it is produced by muscular contractility.
10. Strange as it may seem, after what has been said, some observers maintain that the eilia have no real existence, even in cases where the appearance of them is the most Perfect, and that the whole is an optical de C'eption. I allude particularly to liaspail ; according to him the water which quits the respiring surfaces has, in consequence Of the change produced in it by respiration, acquired a different density, and consequently a dif ferent refractive power from the surrounding fluid ; it therefore produces the appearance of lines or streaks at the surface of the parts, which streaks are the supposed cilia. It is scarcely necessary to repeat that the cilia are Seen when at rest, when all motion of the water has ceased, and that they are evident in circumstances in which no interchange of ma terials can take place between the tissue and the 'wafer in contact with it; and indeed, after the details already given, it is needless to say More' in refutation of this view.