XXXIV. 



ON THE PEESENCE OF CILIA OX THE TADPOLE OF THE 



COMMON FROG. 



By E. B. CfiOFT, E.K, F.L.S., F.E.M.S., Hon. Sec. 



Read at Watford, I9th April, 188L 



FoK several years past I have been of opinion that the exterior 

 cuticle of the tadpole of the common frog (^Hana temporaria) was 

 minutely ciliated. I therefore, early last spring, requested the 

 co-operation of one of our members, Mr. George Turner, in de- 

 termining whether this was the case or not. The tadpoles Mr. 

 Turner had under observation were more advanced than those 

 which came under my notice ; and before any of the ova of my 

 tadpoles were hatched he informed me that he had detected cilia, 

 and had succeeded in mounting sections showing them very clearly. 

 Also that on cutting off the head of a tadpole the tail had been 

 kept in motion for a considerable time by means of the cilia. 



On the hatching of the ova which I had collected I placed some 

 of the young tadpoles in cells, and on adding chloroform to the 

 water in which they were confined I was able, with a ^J-inch ob- 

 jective, distinctly to see that the whole of the exterior cuticle, 

 including that of the gills, was covered with minute vibratile cilia. 



I have reason to believe that this fact has not been previously 

 recorded. At all events it is not mentioned in either Professor 

 Mivart's work on ' The Common Frog,' nor in the article " Com- 

 mon Frog " in Professor Huxley's 'Practical Biology.' We were 

 not able to detect the precise time of the retraction of the cilia, but 

 believe it to have been coincident with the withdrawal of the 

 external gills. 



Postscript, Octoher, 1881. — Since I communicated the above to 

 the Societv, the second volume* of Mr. F. M. Balfour's elaborate 

 ' Treatise on Comparative Embryology ' has been published. In 

 writing on the embryology of the tadpole (p. 205) he says: " The 

 outer layer of the epiblast-cells beconaes ciliated after the close of 

 the segmentation, but the cilia gradually disappear on the forma- 

 tion of the internal gills. The cilia cause a slow I'otatory move- 

 ment of the embryo in the egg, and probably assist in the respira- 

 tion after it is hatched. Ihey are especially developed on the 

 external gills." 



* The first volume, on the Invertebrata, was published in 1880; the second, 

 on the Vertebrata, in 1881. Mr. Croft expressed his suspicion that the epidermis 

 of tlie tadpole of the frog was minutely ciliated in a note in ' Science Gossip ' for 

 April, 1878 (p. 90).— Ed. 



