Section 66. Through Connective Tissues Wander the Phagocytes,

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.