posterior and anterior to it
respectively, the sebaceous glands (oil glands) connected with the
hair, and the anal and perineal glands. The secretions of excretory
glands are removed from the body; chief among them are the sweat
glands and kidneys. The sweat glands are microscopic tubular
glands, terminating internally in a small coil (Figure VIII. s.g.) and
are scattered thickly over the body, the water of their secretion being
constantly removed by evaporation, and the small percentage of salt
and urea remaining to accumulate as dirt, and the chief reasonable
excuse for washing. The kidney structure is shown diagrammatically
in Figure 5, Sheet 7. A great number of branching and straight looped,
tubuli (little tubes) converge on an open space, the pelvis. Towards
the outer layers (cortex) of the kidney, these tubuli terminate in little
dilatations into which tangled knots of blood-vessels project: the
dilatations are called Bowman's capsules (B.c.), and each coil of
bloodvessel a glomerulus (gl.). In the capsules, water is drained from
the blood; in the tubuli, urea and other salts in the urine are secreted
from a branching network of vessels.

Section 63. In all the epithelial tissues that we have considered we
have one feature in common: they are cells, each equivalent to the
amoeba, that have taken on special duties-- in a word, they are
specialists. The amoeba is Jack of all trades and a free lance; the
protective epidermal cell, the current-making ciliated cell, the bile or
urea-making secretory cell, is master of one trade, and a soldier in a
vast and wonderfully organized host. We will now consider our second
kind of cell in this organization, the cell of which the especial aim is
the building round it of a tissue.

Section 64. The simplest variety in this group is hyaline (i.e. glassy)
cartilage (gristle). In this the formative cells (the cartilage
corpuscles) are enjellied in a clear structureless matrix (Figure XII.),
consisting entirely of organic compounds accumulated by their
activity. Immediately round the cell lies a capsule of newer material.
Some of the cells have recently divided (1); others have done so less
recently, and there has been time for the interpolation of matrix, as
at 2. In this way the tissue grows and is repaired. A thin layer of
connective tissue (see below), the perichondrium, clothes the
cartilaginous structure.

Section 65. Connective tissue (Figure XIII) is a general name