Discussion

Abstract

Concerning the methods employed in this investigation into the development of the lymphatic system, it was already stated that the single morphological criteria, used in the identification of lymphatics, were mostly not decisive, especially in the younger embryos. Thus the question arises if these criteria lead to reliable interpretations of the observations. As was stated before, they mostly proved to be of variable value. The most important criterion to differentiate veins from lymphatics was based upon the fact that venous networks communicate with the large veins by wide openings, whereas connections between the lymphatic plexuses and the veins either seem to be completely absent, or are very few in number, in which cases they occur at some special sites and have a very characteristic, split-like, form. In addition, more peripherally too, no connections with the venous plexuses are established in spite of the fact that both structures are practically interwoven. Evidently, it is rather difficult to ascertain such behaviour of both types of vessels, although it proved to be possible by following them in complete series of slides.