628 



CILIA. 



observations on the velocity and direction of 

 the motion, and its supposed influence in de- 

 termining the figure of the animal, I must refer 

 to the paper itself. 



The analogy of these motions of the embryo 

 of the Mollusca with the phenomena exhibited 

 by the ova of Infusoria, Polypi, Sponges, and 

 Actiniae, already described, scarcely requires to 

 be pointed out. We shall afterwards see that 

 it extends to the ova of Batrachian Reptiles.* 



11. Phenomena of the ciliary motion in the, 

 Vertebrata. The ciliary motion exists very ex- 

 tensively in vertebrated animals. Until lately 

 it had been found only in the larvee of Batra- 

 chian Reptiles, but Purkinje and Valentinf 

 have recently made the important discovery 

 that it exists also in adult Reptiles, Birds, and 

 Mammiferous animals; and it seems to prevail 

 generally throughout the three classes, having 

 been found by these naturalists in all the nume- 

 rous examples of each class examined by them 

 in the course of their investigations. It has 

 not been found in Fishes, though many species 

 have been submitted to examination .J 



The parts of the body which exhibit the 

 ciliary motion in the Vertebrata are, the lining 

 membrane of the respiratory organs, and that of 

 the generative organs in the female. Besides 

 this general situation, it is found on the external 

 gills and surface of the body in the larvae of 

 Batrachia, and on the surface of the embryo of 

 these reptiles while contained within the ovum. 



A. Reptiles. The 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 

 branchiae, 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 



* In the preceding account of the ciliary motions 

 in the Invertebrata no mention has been made of 

 their existence in the class Crustacea : I think it 

 necessary to state that I have examined this class, 

 but without success ; and since these pages have 

 been put into the printer's hands I have re -exa- 

 mined the crab and lobster with the greatest care, 

 all the respiratory and alimentary surfaces, the 

 inner surface of bloodvessels, &c. with lenses of 

 all powers, but without finding the phenomenon. I 

 suspect the respiratory currents in Crustacea which 

 are produced by the motion of the branchiae them- 

 selves, or of the plates or oars with which many 

 are provided in order to renew the water, have been 

 confounded with the currents produced by cilia, 

 more especially as many of the organs employed 

 for the purpose in the Crustacea are fringed with 

 long hairs ; but I would scarcely reckon such mo- 

 tion as ciliary any more than those occasioned by 

 the gill-covers ot a fish. 



t Muller's Archiv. 1834. Edinb. New Philos. 

 Journal, xix. and Comm. Phys. de Phenomeno 

 motus vibratorii continui. Wratislav. 1835, 4to. 



J See note at p. 29. 



wholly external, projecting backwards and out- 

 wards from the side of the neck. The tadpole 

 of the Frog (Jig. 309) has at first gills resem- 



Fig. 309. 



Larva of Frog. 



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- 



* Analektenneuer Beobachtungen und Untersuch- 

 ungen fiir die Naturkunde, Furth, 1802. p. 46, 

 sqq. 



