Tonsils belong to the mucosa associated lymphoid tissue (MALT), but because they are incompletely encapsulated, they are considered organs and will be studied apart from the MALT. The tonsils constitute a lymphoid tissue that lies beneath, and in contact with, the epithelium of the initial portion of the digestive tract. Depending on their location, tonsils in the mouth and pharynx are called palatine, pharyngeal, or lingual.
Palatine Tonsils
The two palatine tonsils are located in the lateral walls of the oral part of the pharynx. They are lined with a squamous stratified epithelium that often becomes so densely infiltrated by lymphocytes that it may be difficult to recognize. The lymphoid tissue in these tonsils forms a band that contains free lymphocytes and lymphoid nodules, generally with germinal centers. Each tonsil has 10–20 epithelial invaginations that penetrate the tonsil deeply, forming crypts, whose lumens contain desquamated epithelial cells, live and dead lymphocytes, and bacteria. Crypts may appear as purulent spots in tonsillitis. Separating the lymphoid tissue from subjacent structures is a band of dense connective tissue, the capsule of the tonsil. This capsule usually acts as a barrier against spreading tonsillar infections.

Pharyngeal Tonsil
The pharyngeal tonsil is a single tonsil situated in the superior— posterior portion of the pharynx. It is covered by ciliated pseudostratified columnar epithelium typical of the respiratory tract, although areas of stratified epithelium can also be observed.
The pharyngeal tonsil is composed of pleats of mucosa and contains diffuse lymphoid tissue and lymphoid nodules. It has no crypts, and its capsule is thinner than the capsule of the palatine tonsils. Hypertrophied pharyngeal tonsils resulting from chronic inflammation are called adenoids.

Lingual Tonsils
The lingual tonsils are smaller and more numerous than the palatine and pharyngeal tonsils. They are situated at the base of the tongue and are covered by stratified squamous epithelium. Each lingual tonsil has a single crypt.

Waldeyer's Ring of Lymphoid Tissue
The lymphoid tissue that surrounds the opening into the respiratory and digestive systems forms a ring. The lateral part of the ring is formed by the palatine tonsils and tubal tonsils (lymphoid tissue around the opening of the auditory tube in the lateral wall of the nasopharynx). The pharyngeal tonsil in the roof of the nasopharynx forms the upper part, and the lingual tonsil on the posterior third of the tongue forms the lower part.
Junqueira's Basic Histology: Text and Atlas, 13th Edition
Wheater's Functional Histology: A Text and Color Atlas, 5th Edition