From Raphael Meldola   18 April 1879

My dear Mr. Darwin,

In reply to the question in your last esteemed letter I regret to say that I can only give you a conjectural reply as Fritz Müller does not furnish any information on the habits of the branchiated Trichopteron which I sent to you.¹ You wish to know how the insect keeps its branchiæ moist. Many years ago Newport described I believe a branchiated Trichopteron which frequented the rocks near waterfalls—² F. Müller’s insect may have a similar habit, I do not exactly know where to lay my hands on Newport’s memoir but I will look up the matter before the next meeting of the Entom. Soc. at which the specimen will be exhibited.³ I may add that so far as I remember Newport comes to the conclusion that the supposed branchiæ are really external spiracles.⁴ When we bear in mind how injurious it is to insects to have their spiracular openings stopped with water (which owing to the capillary nature of the spiracular tubes would be most obstinately retained) & connect this with the fact that the larvæ & pupæ of the Trichoptera are aquatic & that the imagos must consequently be often exposed to death by drowning unless provided with some special means of aquatic respiration, we see how natural selection would take advantage of any modification of the spiracles in the direction required for this purpose.

With respectful compliments, | Yours very sincerely, | R. Meldola.