Descartes (Dioptrique, 1637) describes microscopes wherein a concave mirror, with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.
2) shows: the mouth (m), continuous on either side with the groove between the two series of tentacles; the anus (a), in the middle line, at no great distance from the mouth; a transversely elongated epistome (ep), between the mouth and the anus; and, in the concavity of the lophophore, the apertures of the nephridia (n.o.) which, according to De Selys-Longchamps, open into the two large sensory or glandular "lophophoral organs " the orifices of which are seen at gl.
Humped cattle are widely spread over Africa, Madagascar and India, and form a distinct species, Bos indicus, characterized by the presence of a fleshy hump on the shoulders, the convexity (instead of concavity) of the first part of the curve of the horns, the very large size of the dewlap, and the general presence of white rings round the fetlocks, and light circles surrounding the eyes.
As this arrangement extends also to the margins, the wings are more or less twisted upon themselves and present a certain degree of convexity on their superior or upper surface, and a corresponding concavity on their inferior or under surface, - their free edges supplying those fine curves which act with such efficacy upon the air in obtaining the maximum of resistance and the minimum of displacement.
At Arcachon they are arranged in piles each layer being transverse to the one below, so that the space formed by the concavity of the tile is kept open.