Darwin Correspondence Project

Germantown

June 17th— 1855

Dear Sir

I received your welcome note of May 2d and with great pleasure give you all the information in my power relating to the curious history of the water beetle, (Dyticus marginalis) which conveys the eggs of fish from place to place on its fins— I remember distinctly, relating to you, during our pleasant walk, the incidents so interesting to me, and the solution of the dark question of how our Mountain Lakes were peopled by the Lake trout, when these lakes had no inlet above ground, and these fish are never seen in shallow water or in the outlets of these lakes.

My first impression that the D. marginalis was the agent that conveyed the eggs of fish from lake to lake, was received from a story told, I believe, by Kirby, of a Mr Smith, in England, who caught one of this species, in his study, and finding it to belong to the water, put it into a glass jar, where it lived for some time, on examining it the next day he found eggs, floating in the water, which had been adhereing to the fins of the beetle, these eggs soon hatched, and became fish of the same species, which inhabited a neighbouring lake.

In 1846 I had the pleasure of studying the history of this insect, on the shores of several of our mountain lakes in north Pennsylvania, and found that it fed on fish and the fish roe that it found near the margin of these Lakes, destroying numbers of the lake trout which are found only in these inland seas, in deep water, and never in the outlets, most of these lakes are supplied with water by springs at the bottom, only, and have no communication with other lakes, emptying into rivers, where lake trout are never seen.

While on a visit in Montrose, Susquehanna Co Pennsylvania, I was presented with a Dyticus marginalis, which flew into a window, attracted by the light of a lamp, he must have flown at least three miles, as there is no lake nearer that town, but several of some miles in extent about that distance from Montrose— this specimen had no roe on it—but those feeding on the margin of the lake were covered with it—leaving no doubt in my mind as to the fact that they thus carried the eggs, from lake to lake and peopled them with fish that had no other means of being transported—

If this meagre account can throw any light on the subject be assured it will give me much pleasure, and will continue to persue the subject if it continues to interest naturalists, it will make me most happy to communicate with you on this subject, or any other question in natural history that may have fallen under my observation.

The answer to your inquiry of our friends Mr and Mrs Petre, is a sad one, Mr Petre died in Phila soon after your departure from America, and his wife, after many wanderings, has at length gone to Rome, where, a few months since, she professed herself a pervert to the Papal faith—honoured by the Pope with a procession and a Te Deum. How one who worshiped her own mental power so devoutly—could stoop to the thraldom of Rome, is past my finding out, but so it is— I grieve for her sad mistake as she is really a lady of many fine and noble virtues, and was calculated to do much good.

Your Phila friends often think of you with pleasure, amongst the rest Dr Elvin will hear of your where abouts with interest as I heard him conjectureing where you could be, only a few months since—

My Sister joins me in kind remembrance | and believe me | Very respectfully | M H Morris.
Dr R C Alexander | London.