630 



CILIA. 



the detached parts, as it had done previous to 

 their separation. 



At the time of making these observations 

 I had not been able to detect Cilia in these 

 larvse, although, from the analogy of the In- 

 vertebrata, I was led carefully to look for them. 

 Since then I have succeeded in perceiving 

 them with the aid of Wollaston's doublet of 

 one-thirty fifth of an inch focus, especially when 

 a portion of the gill is compressed under a plate 

 of mica. They are to be distinguished chiefly 

 by their waving motion, which is so charac- 

 teristic as to remove all doubt of their ex- 

 istence ; though here, as in other instances in 

 which they are very minute, it is not always 

 possible to demonstrate their existence by 

 actual observation on every spot of the sur- 

 face. 



Ova of the Batrachia. In the course of 

 the above-mentioned observations, I was led 

 to enquire whether the phenomena in question 

 appeared at a still earlier stage. With this 

 view I examined the ova of the Newt, which 

 for a considerable time may be procured in all 

 degrees of advancement, and found that the 

 ciliary motion presented itself in the embryo 

 a considerable time before its exclusion from 

 the egg. Since then I have observed the same 

 with regard to the embryo of the Frog. 



In both cases the embryo is formed from 

 the yolk or opaque central part of the ovum, 

 by a series of changes sufficiently well known ; 

 it is surrounded by a clear fluid, which is 

 inclosed between it and the external pellucid 

 membrane of the egg. By means of a lens, 

 minute bodies may generally be perceived 

 floating in the fluid, which by their motion 

 serve to indicate the currents that take place 

 in it; but with a little care the embryo may 

 be extracted from the egg, and then the course 

 of the currents along its surface can be ren- 

 dered more evident by the usual means. 

 A (Jig. 310) is an enlarged view of the embryo 



Fig. 310. 



Embryo of the Frog. 



of the Frog at the earliest stage at which I have 

 detected the motion. The vertebral canal is 

 just closed, and at the fore part of the body 

 three ridges on each side indicate the com- 

 mencement of the gills. The arrows point out 

 the course of the currents. They proceeded 

 backwards along the dorsal surface, diverging 

 in a direction downwards and backwards on 

 the sides. They were visible but weaker on 

 the abdominal surface. B represents the em- 

 bryo farther advanced, the currents have nearly 

 the same direction but are better marked, they 

 are strongest on the lateral eminences of the 



head which correspond to the future gills. 

 In the embryo of the Newt, the phenomena 

 are in a great measure similar ; the currents 

 seemed, however, to begin and to continue most 

 vigorous on the abdominal surface; they are 

 more particularly described in the paper re- 

 ferred to. 



On extracting the embryo of the Frog, and 

 viewing its surface in profile with Wollaston's 

 doublet, moving cilia may be perceived on 

 various parts. They appear like a transparent 

 undulating line on the surface, and, though 

 very minute, are so distinct as to leave no doubt 

 of their existence. 



No one can fail to perceive the analogy 

 which subsists between the phenomena just 

 described, and those which occur in the ova 

 of Zoophytes and Mollusca. I have not been 

 able distinctly to perceive a rotation of the 

 embryo of the Batrachia, as observed in the 

 other instances, but Purkinje and Valentin 

 state that they have seen it, and Rusconi ob- 

 served that the embryo of the Frog, when 

 extracted from the ovum, turned round in a 

 certain direction, which motion he supposed 

 to be produced by water entering and issuing 

 through pores in the skin.* 



The phenomena in the Batrachian larvae have 

 since been observed by Muller,f Raspail,J 

 and Purkinje and Valentin. The last men- 

 tioned naturalists also distinguished the cilia 

 and perceived the motion within the egg. 



Adult Batrachia. The ciliary motion was 

 discovered in the adult Batrachia by Purkinje 

 and Valentin ; indeed, it may not be improper 

 again to state that the discovery of the phe- 

 nomena in adult Reptiles generally, and in Birds 

 and Mammiferous animals, is due to these phy- 

 siologists. 



According to their account, the ciliary mo- 

 tion in the Batrachia, as well as in all other 

 vertebrated animals in which they have dis- 

 covered it, occurs in two situations within 

 the body, viz. on the lining membrane of the 

 respiratory organs and on that of the genital 

 organs of the female. They state that it exists 

 over the whole internal surface of the lungs, 

 and in the nose, mouth, and pharynx, extend- 

 ing as far back in the throat as the glottis, but 

 no farther. They say nothing of the direction 

 of the impulsion. Again, in the female, they 

 discovered the motion on the internal surface 

 of the oviduct. The result of my own ex- 

 amination of the Newt, Frog, and Toad is 

 somewhat different. In all the three I found 

 the ciliary motion very distinct in the mouth, 

 throat, and gullet ; in none could I perceive it 

 in the lungs, notwithstanding very careful trials. 

 In regard to the oviduct I have examined it 

 only in the Newt, and although I could per- 

 ceive something like the motion on the edges 

 of its superior orifice, I could not detect it on 

 the internal surface of the tube.|| 



* Sur le Developpement de la Grenouille Com- 

 mune. Milan, 1826. 



f Burdach's Physiologic, Bd. iv. p. 434. 



t Chimie Organique, 1833, p. 250. 



Op. cit. 



II Edin. New Phil. Journal, xix. 



