Lymphatic tissue is rich in lymphocytes (and accessory cells such as macrophages and reticular cells). The lymphatic tissue includes the lymph nodes, spleen, tonsils, adenoids and the thymus (an organ in the chest that is particularly large during infancy).
The term musical form (or musical architecture) refers to the overall structure or plan of a piece of music; it describes the layout of a composition as divided into sections. In the tenth edition of The Oxford Companion to Music, Percy Scholes defines musical form as a series of strategies designed to find a successful mean between the opposite extremes of unrelieved repetition and unrelieved alteration.
Theme and variation is a specific kind of form in music. The form of a piece of music tells you how the music is organized. With a theme and variation, the piece begins with a theme that is the main melody. That is followed by one or more variations of that melody.