Altogether commendable is the spirit which leads a boy or girl to collect and arrange shells, common wildflowers, seaweeds, and the diverse minerals brought to light in a railroad cutting. What is thus gathered, compared, and studied will leave a much deeper impression on the memory than what is seen for a moment in a museum or a public garden. And yet, to the profound student the museum is indispensable: he gives weeks or months to the contents of its cases, supplementing what he has learned in the field, by the seashore, in the woods. Take, for example, protective resemblances, one of the most fascinating provinces of natural history. Here is a hornet clear-wing moth. What has made it look like a wasp? Both share the same field of life, and while the wasp does not prey on the moth or in any perceptible way compete with it, the two insects have a vital bond. In its sting the wasp has so formidable and thoroughly advertised a weapon that by closely resembling the wasp the moth, though stingless, is able to live on its neighbor’s reputation, and escape attack from the birds and insects which would devour it if they did not fear that it is a stinging wasp. So far is the resemblance carried that when the moth is caught in the hand it curves its body with an attitude so wasplike as seriously to strain the nerves of its captor. How came about so elaborate a masquerade? At first, ages ago, there was a faint likeness between the moth and the wasp; any moth in which that likeness was unusually decided had therein an advantage and tended to be in some measure left alone by enemies. In thus escaping it could transmit in an ever-increasing degree, its peculiarities of form and hue to its progeny, until in the rapid succession of insect generations, amid the equally rapid destruction of comparatively unprotected moths, the present striking similarity arose. Instances of this kind abound, forming some of the most attractive exhibits in the American Museum of Natural History of New York, and other great museums. Mr. W. H. Bates, who first explained these resemblances, did so as the result of comparing many various examples preserved in his cabinets at home, although, of course, his memory of habits observed in the field was indispensable. His ample collections enabled him to bring into view at once many captures separated by wide intervals of time and space. It was the opportunity thus afforded of taking a comprehensive survey of resemblances as a whole that led him to think out the underlying reason. Accidental Observation.