EXPLANATION OF THE PLATES. 



PLATE XXI. 



Fig. 1. Ciliary epithelium from the trachea of the frog ; it 

 will be seen that the form of the cells is very dif- 

 ferent from that of mammalia. 



Fig. 2. Human ciliary epithelium contained in the fluid ex- 

 pressed from a portion of lung taken from its ex- 

 treme periphery, and apparently consisting of air- 

 cells alone. It is mixed up with cells of tesselated 

 epithelium. 



Fig. 3. Human ciliary epithelium from the trachea ; both 

 side and end views of the cells are given. 



Fig. 4. Tesselated epithelium from the tongue of the frog. 



Fig. 5. Tesselated epithelium from the tongue of the Triton : 

 the nuclei are seen to be very large, their great size 

 affording an illustration of the law which has already 

 been announced, viz. that all the corpuscular ele- 

 ments of the animal organisation, whether those of 

 the epithelium, the glands, cartilages or muscles 

 stand in relation with the dimensions of the blood 

 discs ; where these are large, the other corpuscles 

 are formed on a similar relative scale. 



It is probable that the law admits of extension, 

 and that all the elements of the animal structure 

 bear a relation in size to the red blood discs. 



Mr. John Quekett made the interesting observ- 

 ation, some time since, that the relative size of the 

 lacuna? of bone corresponded with that of the blood 

 corpuscles, a further illustration of the accuracy of 

 the law referred to. 



