A. ciliary motion has been discovered in all the orders of Reptiles. It has been found in every species submitted to ex amination, and is therefore presumed to exist in all.
Batrachian Reptiles. 1st. Larva and ova. —The Batrachian Reptiles, -while in the foetal or larva state, breathe by means of -gills or branchim, and it was on the gills of the young Salamander and Frog that the phenomenon under consideration was first discovered as existing in vertebrated animals. The gills of the young Salamander might in appearance be compared to feathers or pinnated leaves; there are three on either side, each consisting of a main stem bearing two rows of simple leaflets; they are wholly external, projecting backwards and wards from the side of the neck. The tadpole of the Frog (fig. 309) has at first gills resem bling those of the Salamander, but of a simpler form; they are also three on each side, but have each only five or six diverging branches. The gills of the Salamander, although not perma nent, endure till the animal makes full use of its lungs, but the external gills of the Frog are of very short duration, being soon superseded by internal gills, more resembling those of a fish, with which the animal respires for the rest of the larva state.
By means of the microscope the blood may be seen circulating through the external gills of the Frog and Salamander ; it passes outwards to their extremities by the branchial arteries, and returns in a contrary direction by the branchial veins. The water also is moved continually over these organs, for the purpose of respira tion, in a constant and determinate direction, and this is effected by the peculiar impelling power we are here considering, viz. the ciliary motion on their surface.
Steinbuch,* a German naturalist already mentioned, while examining the circulation of the blood in the gills of the Salamander, ob served that small bodies floating in the water were carried, as if by attraction, to the surface of the gill, and again repelled from it. He also found that portions detached from the gill moved themselves through the water, or if kept fixed, continued as before to attract and repel small objects in their vicinity. From these and similar facts he was led to conclude that the water was continually propelled over all parts of the gill, that the current thus produced served to renew the water in the process of re spiration, that the power producing the propul sion resided in the gill, and was exercised in dependently of the will of the animal ; and lastly, from the analogy of infusoria and Polypi, in which currents are produced by cilia, he in ferred that in this case also the water was pro bably impelled along the surface by the action of cilia, though he could not actually perceive any such organs. Steinbuch next examined
the tadpole of the Frog, and found that its ex ternal gills exhibited the same phenomena, but be could discover nothing of the kind. on the internal gills.
Gruithuisee observed in the tadpole of the Green Frog that so soon as the circulation of the blood began in any part of the gills, small ob jects were attracted and repelled from that spot, and that the same took place a few days later on the tail wherever vessels had been formed. He conceived that the motion of the water was for the purpose of exposing the blood to its in fluence, and. compared it to the current pro duced by Infusoria by means of cilia. He does not say, however, that he had seen cilia in the tadpole.
Huschket observed that the water in the vicinity of the gills of the young Salamander was thrown into a boiling-like motion, while it flowed steadily at other parts of the body.
Without being aware of these previous disco veries, I was led in 1830, by an accidental ob servation of my own, to go over nearly the same ground.t I had cut off one of the external gills of the tadpole of the Frog, and placed it with a drop of water under the microscope, with the view of measuring the size of the glo bules of blood that might flow from it, and was astonished to perceive that the globules, on escaping from the cut part of the gill, moved rapidly along its surface towards the points of the branches in a constant and uniform manner. On further inspection it soon became evident that the blood-globules were entirely passive in their motion, and that other light particles brought near the gills were moved in a similar manner; their motion being manifestly owing to a current produced in the water along the surface of the gill in a determinate direction. A conclusive proof of this was afforded by put ting the gill which had been cut off, into a watch-glass with a larger quantity of water. It was then seen that when the gill happened to be fixed by any obstacle, small bodies in its vicinity were moved along it as before towards the points of the branches, but when unim peded the gill itself advanced through the water in a direction contrary to that in which the particles were moved, the trunk being turned forward ; the tendency to produce a current in one direction, thus causing the gill, now no longer fixed, to move in the opposite one. The current began at the root of the gill, and ran along the branches, at the points of which it did not continue its primitive direc tion, but turned off sideways, and immediately ceased. (See fig. 309, C).