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Darwin Correspondence Project

To M. A. T. Whitby   12 August [1849]1

Down Farnborough Kent

Aug. 12th

My dear Madam

I cannot express too strongly my thanks for the extraordinary trouble which you have taken in the interesting experiment, of which you send me the result.—2 I had given up all hopes of knowing whether peculiarities in the caterpillar state were hereditary, but now the point is amply proved: there is indeed a wide difference between a probability, however high & such an experiment as you have made.—

I am, also, much obliged for the information about the S. French caterpillar breeds; I was not aware the differences were so great.3

If it would not be asking too great a favour, I shd be greatly obliged if you would take the trouble to inform me, should you ever observe anything remarkable in the hereditary principle, or in the differences in structure or habits between breeds in the Silk-worm.— I dare not do more than hint my curiosity to know whether the Frales4 would prove hereditary,—ie whether it would be possible to make a breed with cocoons destitute of silk.—5 In the eyes of all silk-growers, this assuredly would appear the most useless of experiments ever tryed.—

Pray accept my most cordial thanks, & believe me with much respect, | Your’s sincerely obliged | C. Darwin


The date is based on the broad mourning border characteristic of the stationery used by CD in 1849.
See CD’s request in his letter to M. A. T. Whitby, 2 September [1847]. He cited the results in Variation 1: 302.
Whitby 1848 mentions cocoons from eggs imported from Bordeaux and Poitiers. A table indicates that these cocoons gave 134 oz. of reeled silk, whereas the equivalent weight of cocoons of English and Italian species yielded 14 oz. and 1 oz., respectively (pp. 56–7).
See letter to M. A. T. Whitby, 2 September [1847], in which CD asked about the possibility of conducting an experiment to see if ‘frales’ would reproduce their kind. The original manuscript reads ‘Frates’, but from CD’s letter of 2 September [1847] it is clear that this is another instance of his unintentional crossing of an ‘l’.
According to Variation 1: 303, ‘Cocoons are sometimes formed, as is well known, entirely destitute of silk, which yet produce moths; unfortunately Mrs. Whitby was prevented by an accident from ascertaining whether this character would prove hereditary’.


Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.

Whitby, Mary Anne Theresa. 1848. A manual for rearing silkworms in England: with a brief notice on the cultivation of the mulberry tree. London.


Thanks MATW for the results of her experiments on the inheritance of caterpillar peculiarities and would be grateful for any further observations on differences in structure or habits between silkworm breeds, or peculiarities in inheritance.

Letter details

Letter no.
Charles Robert Darwin
Mary Anne Theresa Whitby
Sent from
Source of text
New York Academy of Medicine (MS 15)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 1194,” accessed on 4 March 2021,

Also published in The Correspondence of Charles Darwin, vol. 4