122 EVOLUTION [CHAP. Ill 



Letter 73 of the pyramidal basal plates are contrasted. Will you 

 oblige me by looking with a strong lens at the bit of comb, 

 brushing off with a knife the upper thickened edges, and then 

 compare, by eye alone, the thickness of the walls there with 

 the thickness of the basal plates, as seen in any cross section. 

 I should very much like to hear whether, even in this way, 

 the difference is not perceptible. It is generally thus per- 

 ceptible by comparing the thickness of the walls of the 

 hexagon (if not taken very close to the angle) near to the 

 basal plates, where the comparison by eye is of course easier. 

 Your letter actually turned me sick with panic ; from not 

 seeing any great importance [in the] fact, till I looked at my 

 notes, I did not remember that I made several measurements. 

 I have now repeated the same measurements, roughly with 

 the same general results, but the difference, I think, is hardly 

 double. 



I should not have mentioned the thickness of the basal 

 plates at all, had I not thought it would give an unfair 

 notion of the thickness of the walls to state the lesser 

 measurements alone. 



Letter 74 To W. H. Miller. 



[1859] 



I had no thought that you would measure the thickness 

 of the walls of the cells ; but if you will, and allow me to give 

 your measurements, it will be an immense advantage. As it 

 is no trouble, I send more specimens. If you measure, please 

 observe that I measured the thickness of the walls of the 

 hexagonal prisms not very near the base ; but from your very 

 interesting remarks the lower part of the walls ought to be 

 measured. 



Thank you for the suggestion about how bees judge of 

 angles and distances. I will keep it in mind. It is a com- 

 plete perplexity to me, and yet certainly insects can rudely 

 somehow judge of distance. There are special difficulties on 

 account of the gradation in size between the worker-cells and 

 the larger drone-cells. I am trying to test the case practi- 

 cally by getting combs of different species, and of our own 

 bee from different climates. I have lately had some from 

 the W. Indies of our common bee, but the cells seem certainly 

 to be larger; but they have not yet been carefully measured. 



