LYMPHATICS IN THE LUNG OF A PRECOCIAL BIRD BEFORE AND AFTER HATCHING

A light and electron microscopic study of pulmonary lymphatics was car ried out in quail embryos (embryonic day; ED 13-17), completed with sa mples of lungs of quail 90 min, 24 h after hatching and two 2-day-old and three adult quail. The aim of the study was to depict the morpholo gy of pulmonary lymphatics by determining the dynamics in ontogeny and to establish the rules of their distribution. The primitive lymphatic s appear on ED 13 and 14 as closed thin-walled tubes in abundant inter parabronchial mesenchyme. They seemingly differentiate from the mesenc hymal cells. Due to the proliferation, growth, and enlargement of the parabronchial compartments, the interparabronchial septa disappear to a large extent, and the external walls of parabronchi appose and join. On ED 16 and 17, the mesenchyme is squeezed to the trigonal fields am ong the neighboring parabronchi. The lymphatics form broad, voluminous lakes around the arteries; on the other hand, they are also found in close contact with the gas exchange tissue as juxta-air capillary lymp hatics. After hatching, the former interparabronchial septa disappear, and the imaginary boundary between parabronchi is demarcated by inter parabronchial arteries and veins. The lymphatics are confined to the a dventitial connective tissue which conducts rite larger arteries and v eins of the original trigone of the interparabronchial septa. The rich ly vascularized parabronchi in mature quail are poor in connective tis sue and to a large extent devoid of lymphatics, in comparison to the m ammalian lung where rite lymphatic capillaries have their roots at the level of the respiratory bronchioles. The avian pulmonary lymphatics serve as an appropriate model for the analysis of principles controlli ng the origin and distribution of lymphatics in general.