cells that are difficult to distinguish, if really distinct, from the white
blood corpuscles. These cells possess a remarkable freedom; they
show an initiative of their own, and seem endowed with a
subordinate individuality. They occur in great numbers in a tissue
called, botryoidal tissue (Figure XIV.), which occurs especially in
masses and patches along the course of the alimentary canal, in its
walls. The tonsils, swellings on either side of the throat, are such
masses, and aggregates occur as visible patches, the Peyer's
patches, on the ileum. It also constitutes the mass of the vermiform
appendix and the wall of the sacculus rotundus; and in the young
animal the "thymus gland," ventral to the heart, and less entirely, the
"thyroid gland," ventral to the larynx, are similar structures, which
are reduced or disappear as development proceeds. It is evident that
in these two latter cases the term "gland" is somewhat of a
misnomer. The matrix of botryoidal tissue is a network of stretched
and hollowed connective tissue cells-- it is not a secretion, as
cartilage matrix appears to be. During digestion, the phagocytes prowl
into the intestine, and ingest and devour bacteria, that might
otherwise give rise to disease. In inflammation, we may note here,
they converge from all directions upon the point wounded or irritated.
They appear to be the active agents in all processes of absorption
(see osteoclasts under bone), and for instance, migrate into and
devour the tissue of the tadpole's tail, during its metamorphosis to the
adult frog.