process of transformation.

At b the bulb separates into two portions,

namely, the hair and its enveloping sheath. The figure is magnified 38 times.

FIG. 5. A small fragment of the fibrous structure of a hair magnified 310 times.

FIG. 6. A fragment of the pith of a swan's feather, showing its composition of globular cells, very little altered in shape by contact.

FIG. 7. Hair of the fallow deer; magnified 38 times. The middle layer of this hair, instead of being fibrous, is made up of polyhedral cells; which are simple globular cells pressed into an angular form by contact, like the cells of a honeycomb. These hairs are consequently excessively light and brittle.

FIG. 8. A portion of the shaft of a very small pheasant-feather; showing the exact similitude between its pith and the cellulated structure of the hair of the deer.

FIG. 9. Barbs from the vane of a small pheasant-feather, magnified 310 times.

a. Part of a barb from near the shaft of the feather, showing its composition of a series of oblong, flattened cells, with nuclei. b. One of the floating barbs from near the quill: the cells in this figure are longer and more slender than in the preceding, and there is a tendency to division at the upper end of each. c. One of the barbs from the upper end of the feather. It is composed of a series of oblong cells with nuclei, like a, but the cells are more elongated, and are divided at the upper end into two little spurs. When it is recollected that these three modifications occur in a single small feather, modifications it will be perceived of the same essential parts, the mind will be prepared for modifications of a similar kind in the hairy coverings of different animals, and will be able also to trace through such modifications the identity of the original element, a cell.

FIG. 10. Portions of two hairs from the common hare. a. A small hair consisting of a single row of cells enclosed by a transparent envelope of scales. At its upper part this hair is beginning to enlarge in consequence of the division of the single cells into pairs. Further still, a third series of cells (not shown in figure) was introduced with a still further increase of bulk of the hair. This structure forms a transition to b. one of the large hairs, in which a number of series of simple cells are collected together and enclosed in a transparent envelope composed of scales. The smaller hair is magnified 310 times, the larger 155 times. FIG. 11. Hairs of the mouse magnified 310 times. Figure a represents the hair near its root. b. Is taken from a portion of hair further onwards in the shaft where it has become thicker and is still enlarging. The structure, it will be observed, is essentially the same as fig. 10, a series of cells separated by interspaces, and enclosed in an envelope of scales, the latter being somewhat more strongly marked. The enlargement of the hair occurs in consequence of the multiplication of the rows of cells as is seen in the upper part of the figure. Moreover, the cells in the hair of the mouse contain the black pigment which gives the gray colour to its coat. FIG. 12. The hair of the Indian bat magnified 310 times. This hair is remarkable for the curious modification of its external scales. a. Is one of these hairs near its root; at its lower part the peculiarity in the scales is lost, and it bears a resemblance to the structure of a, fig. 9, while above it reminds us of b and c, fig. 9. b. A portion of the same hair higher in the shaft.

c. A portion from the hair at a still higher point. d. One of the

separate scales; two of these complete the circle around the shaft. Near the upper part of a one of the scales is broken away. FIG. 13. Two fibres of linen magnified 155 times. FIG. 14. Two fibres of silk magnified 155 times. FIG. 15. A fibre of cotton magnified 155 times. FIG. 16. A fibre of wool magnified 310 times. hair, and has its characteristic scaly surface. Berlin wool.

This fibre is, obviously, a
The specimen selected is

PLATE 5.

THE ACARUS SCABIEI, OR ITCH ANIMALCULE.

FIG. 1. The animalcule 107 times magnified, and viewed upon its under surface.

FIG. 2. The same animalcule, viewed upon its upper or dorsal surface.

FIG. 3. One of the fore feet of the animalcule magnified 456 times, and viewed upon its plantar aspect.

FIG. 4. Two of the ova of the animalcule magnified 38 times.

PLATE 6.

STRUCTURE OF WARTS AND CORNS, TOGETHER WITH SOME DISEASES OF THE SEBIPAROUS GLANDS.

FIG. 1. Section of a wart, from the arm-pit, magnified 19 times. The enlarged papilla of the sensitive skin, enclosed in conical sheaths of scarfskin, are seen.

FIG. 2. A cluster of the enlarged papilla of the wart, withdrawn from their sheaths of scarf-skin. This figure is magnified, like the preceding, 19 times.

FIG. 3. A portion of the scarf-skin covering of a wart magnified 38 times, and viewed upon its under surface. In this view, the openings of the conical sheaths of the papillæ are seen, and a circle of cells containing an increased proportion of pigment, around the base of each. FIG. 4. The structure of a corn, illustrated by means of a diagram in section. b, b. The sensitive skin surmounted by its papillæ. d, d. The thickened scarf-skin, which is seen to be laminated, and the broad dark streak, e, is the discoloured remains of a stratum of blood, poured out when the matter of the streak rested on the surface of the derma.

FIG. 5. A spine taken from a boy suffering under the "porcupine disease," the whole body was covered with spines of this kind, standing out, nearly perpendicularly, from the surface of the skin. The spine is magnified 19

times.

FIG. 6. A portion of skin, affected with small tumours, caused by enlargement of the sebiparous glands. This is the disease termed "molluscum." e tumours are drawn to the size of nature.

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