30 Mr. II. J. Carter on the Ovigerous Layer of Now remelt the material on the glass slide as before ; and when sufficiently fluidified to present a uniformly level surface (but not burnt, for this would destroy the tenacity of the cement and thus give it a crispness which, by cracking, would defeat all attempts at further reduction), quickly transfer the warmed slice (which should now be close at hand) to it, while with a little pressure the 'â– 'â– smoothed'''' surface is brought into direct contact with that of the glass. Thus let it remain on the table where this is done until the glass feels cold to the touch. After this reduce the slice to the thinness of a wafer over a very fine vertical rotating grinding-stone, or on a copper plate with emery powder and water, horizontally. Now wash it well in water, and, placing the slide on a piece of buckskin leather spread on the table or over a level surface (to keep it from slipping) with the slice uppermost, continue the reduction in water with a piece of very fine siliceous limestone, that may be obtained from a statuary, of a convenient form (that is, one which will admit of the surface of the slice coming into direct and continuous contact with that of the limestone), with which it should be horizontally rubbed until reduced to the required thinness, which must be ascertained by repeatedly transferring the slice to the field of the microscope with an inch object-glass and high ocular. The nearer this thinness is approached the oftener this trans-fer should be made, washing the slice by dipping the slide into a bowl of water each time that it is examined. When sufficiently reduced, wash the slide as before, and stand it up to drain until the slice is perfectly dry. Then cover with benzol, followed by balsam and thin glass, for preservation and more deliberate examination. I make no apology for introducing these remarks, as the " process," although open to criticism and improvement no doubt, answers the purpose ; and while inexperienced I myself should have been very glad of such aid. Dr. Holl suggested to me the use of shellac, which is the most valuable hint that I have received. IV. — On the Presence of Starch-granules in the Ovum of the Marine Sponges, and on the Ovigerous Layer of Suberites domuncula, Nardo, By H. J. Carter, F.R.S. &c. It was but a short time since that I pointed out another in-stance of a structure like that of the cellular tissue of plants,
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