One would think that, with such an array of gills, this larva ought to be in good case for its air-supply. It may, perhaps, be doubted whether this is so. At any rate, the creature adopts the same plan as the larva of Chironomus, which has no gills at all, for driving away from its case water that has parted with its oxygen. Water charged with oxygen pours into the case, and so the air-supply is renewed. This plan is nothing more than keeping the fore-part of the body in undulating motion, the tail in both the larvae serving as a point of attachment. One or two that I have kept made their cases against the side of the bottle, and so afforded an excellent opportunity of seeing them in this motion. The Tanypus larva does the same thing. Against the side of one of my small aquaria a Tanypus larva and a Chironomus larva have both made tubes; and as I look up from writing these lines I can see them both hard at this work. The larva of the Alder-fly (_Si´alis luta´rius_) is also furnished with tracheal gills, seven on each side. So little is known of the life-histories of common insects that it may be profitable to introduce the account of an observer who watched the deposition of the eggs and the emergence of the young larvae: ‘On April 25 I found, on the rushes round the margin of a small pond, a great many patches of eggs, and shortly after observed many of the _Sialis lutarius_ depositing them. ‘They form large patches of from two to three inches in length, generally encircling the whole rush near the top, but sometimes deposited on one side only, and extended to about a line in breadth. ‘I counted 100 in a square line, so that each batch may be fairly considered to contain from 2,000 to 3,000 eggs; the greater portion of which must consequently perish either in the egg or larva state; as, common as the insect is, and widely distributed throughout the country, we should be perfectly overwhelmed with the swarms of the perfect insect if such were permitted, when it is considered that round this one small pond there could not have been less than 100 patches of them. ‘The eggs are of a very singular form, and placed in a slanting position. ‘The females, while depositing them, appeared perfectly motionless on the rush, and varied considerably in size, being from five lines to nearly double that in length. Some parts of the patches of eggs are of a much lighter colour than the rest. ‘On May 3 I found many of the eggs hatching, the little larvae tumbling about in great numbers, with their bodies erected like [the larvae of] the _Staphylinidae_. ‘On putting them into water they swam about with the greatest activity, wriggling and undulating their bodies about much like a serpent or the tadpoles, and working their legs at the same time[66].’ The author draws attention to the disproportionately large head of the larvae, which, however, he did not describe, as he had ‘brought some of them alive, and some eggs for exhibition.’