1 868.] SEXUAL SELECTION. 97 



of his sources of information, and as showing what were the 

 thoughts at this time occupying him :] 



C. Darwin to F. Miiller. 



Down, June 3 [1868]. 



. . . Many thanks for all the curious facts about the unequal 

 number of the sexes in Crustacea, but the more I investigate 

 this subject the deeper I sink in doubt and difficulty. Thanks 

 also for the confirmation of the rivalry of Cicadae. I have 

 often reflected with surprise on the diversity of the means for 

 producing music with insects, and still more with birds. We 

 thus get a high idea of the importance of song in the animal 

 kingdom. Please to tell me where I can find any account 

 of the auditory organs in the Orthoptera. Your facts are 

 quite new to me. Scudder has described an insect in the 

 Devonian strata, furnished with a stridulating apparatus. 

 I believe he is to be trusted, and, if so, the apparatus is of 

 astonishing antiquity. After reading Landois's paper I have 

 been working at the stridulating organ in the Lamellicorn 

 beetles, in expectation of finding it sexual ; but I have only 

 found it as yet in two cases, and in these it was equally de- 

 veloped in both sexes. I wish you would look at any of 

 your common Lamellicorns, and take hold of both males 

 and females, and observe whether they make the squeaking 

 or grating noise equally. If they do not, you could, perhaps, 

 send me a male and female in a light little box. How 

 curious it is that there should be a special organ for an object 

 apparently so unimportant as squeaking. Here is another 

 point ; have you any toucans ? if so, ask any trustworthy 

 hunter whether the beaks of the males, or of both sexes, 

 are more brightly coloured during the breeding season than 

 at other times of the year. . . . Heaven knows whether I 

 shall ever live to make use of half the valuable facts which 

 you have communicated to me ! Your paper on Balanus 



VOL. III. H 



