Another still more remarkable instance of a hinged door in an egg is to be found in one of the Rotifers, or Wheel-Animalcules, so called because they possess an apparatus of movable cilia, which, when set in motion, looks exactly like a wheel running round and round. As the full-grown creature is barely one thirty-sixth of an inch in total length, the structure of its eggs must be infinitesimally beyond the range of human vision. Yet, just as the telescope sets at partial defiance the vast spaces that intervene between our earth and her sister planets, so the microscope performs a similar task in the infinitesimally minute. And, under the all-revealing lens of the microscope, the little egg of the Brachionus, though absolutely invisible to the unaided eye, yields up its secrets. Fortunately, the shell is so transparent that the interior of the egg can be seen through it as if it were a mere film of glass. The astonishing division and re-division of the yolk take place before our eyes, being divided first into two, then into four, then into eight, then into sixteen, then into thirty-two, and so on, until the whole mass of the yolk is cloven into divisions too numerous to count. By degrees, the form of the young Brachionus is developed within the egg, even to the very teeth, which work away as persistently as if large stores of food were being passed through them. When the young is ready to take its place in the world, a new development occurs, which has been well related by Mr. Gosse:-- “All these phenomena have appeared in the egg we are now watching; and at this moment you see the crystalline little prisoner, writhing and turning impatiently within its prison, striving to burst forth into liberty. “Now, a crack, like a line of light, shoots round one end of the egg, and in an instant, the anterior third of the egg is forced off, and the wheels of the infant Brachionus are seen rotating as perfectly as if the little creature had had a year’s practice. “Away it glides, the very image of its mother, and swims to some distance before it casts anchor, beginning an independent life. At the moment of escape of the young, the pushed-off lid of the egg resumes its place, and the egg appears nearly whole again, but empty and perfectly hyaline (_i.e._ all but transparent), with no evidence of its fracture, except a slight interruption of its outline, and a very faint line running across it.” To pass from the egg to a more advanced stage in life. All practical entomologists have been greatly annoyed, in their earlier years of collecting, to lose larva after larva, from the attacks of Ichneumon-flies. It _is_ certainly rather beyond the limits of ordinary patience to discover, watch over, and secure successfully a rare caterpillar, and then to find that it has been “stung” by an Ichneumon-fly.