There is, in birds, no annulus tympanicus.
The annuli into which segments are externally divided are so deeply incised as to render it impossible to distinguish, as can be readily done in the Oligochaeta as a rule, the limits of an annulus from that of a true segment.
Cap. 3) - " Nullus hiatus est, nulla fractio, nulla dispersio formarum, invicem connexa sunt velut annulus annulo "; but it is almost clear that he was thinking only of a chain.
It has been found by Sir William Herschel and others that the definition of a telescope is often improved by stopping off a part of the central area of the object-glass; but the advantage to be obtained in this way is in no case great, and anything like a reduction of the aperture to a narrow annulus is attended by a development of the external luminous rings sufficient to outweigh any improvement due to the diminished diameter of the central area.'
A, the annulus, or remnant of C, longitudinal section of mature velum partiale.
The expression for w in (i) § 29 may be increased by the addition of the term im log z =-m0 + im log r, (1) representing vortex motion circulating round the annulus of liquid.
Ann, Chitinous annulus, containing air cavities which enable the stato blast to float.
Then consider a thin annulus thin of the wire of width dx; the charge on it is equal to thin rod.
21rry/dx units, and the potential V at a point on the axis at a distance x from the annulus due to this elementary charge is ll2 2?rrc V=2 j o (r2+x2) dx=47rrvj log e (2l+1,/ r2 +412 ') - loge'} If, then, r is small compared with 1, we have V =47rry log e llr.
The figure Abdc is a sector of an annulus, which is the portion of a circle left after cutting out a concentric circle.
By unrolling each such element (§ 30) into a sector of a circular annulus, it will be found that the total area of the surface is M'.
A, The annulus, or remnant of B, The mature plant.
The sporangia (pollen-sacs), which occur on the under-side of the stamens, are often arranged in more or less definite groups or sori, interspersed with hairs (paraphyses); dehiscence takes place along a line marked out by the occurrence of smaller and thinner-walled cells bounded by larger and thickerwalled elements, which form a fairly prominent cap-like " annulus " near the apex of the sporangium, not unlike the annulus characteristic of the Schizaeaceae among ferns.
3, C); at the base of the cone an outgrowth of the axis like a rudimentary leaf sheath (the annulus) is present.
The sporangium is of considerable size, and dehisces by a median slit, the annulus being a more or less definitely limited horizontal ring of cells near the apex.
The annulus is horizontal and the dehiscence median.
The sporangium, which corresponds on the whole to that of the Gleicheniaceae, has a somewhat oblique annulus; the dehiscence also is not truly median.
The sporangia, which arise in basipetal succession on the receptacle, dehisce by a median slit, though the annulus is somewhat oblique; they have resemblances to the Gleicheniaceae.
Each has an almost horizontal annulus resembling that of Gleichenia, but the dehiscence is lateral.
The dehiscence of the sporangium is almost transverse, as in the Polypodiaceae, but the annulus is slightly oblique.
The sporangia dehisce by a transverse slit, the annulus being truly vertical or, in some of the genera in which they are regularly arranged, very slightly oblique.
The differences in the form and mode of dehiscence of the sporangia (those of the Simplices having median dehiscence and a horizontal annulus, those of the Gradatae a more or less oblique position of the annulus and of the plane of dehiscence, while in the Mixtae the annulus is vertical and the dehiscence transverse) stand in relation to the position of the sporangia in the sorus relatively to one another.
The absence of an annulus from their indehiscent sporangia makes it impossible to compare them with the other Ferns in respect of this important character.