Structure and Function of the Subcutaneous Lymph Sacs in the Anura (Amphibia)

The gross structure of the subcutaneous lymph sacs was examined in anurans from diverse habitats. There were apparent correlations of large lymph sacs with aquatic habit and of reduced lymph sacs with fossorial habit. It was found that all previous hypotheses concerning the function of the subcutaneous sacs could not explain such correlations. It is proposed that the subcutaneous spaces, in connection with the posterior lymph hearts, renal portal vein and the kidney, form a mechanism for rapidly excreting incoming water. hearts into the anterior vertebral veins, and via the posterior hearts into the renal portal veins. The subcutaneous spaces are characteristic of all anurans yet there have been no comparative surveys of subcutaneous anatomy. Most contemporary authors refer to Ecker's (1881) description of the spaces in Rana esculenta. The fact that such sacs are unique to the Anura indicates they have a special function possibly related to the singular habits and physiology of these animals. Obviously it is unreasonable to generalize about function when detailed anatomical knowledge is confined to one species. Accordingly my investigation began with a survey of the gross sub- cutaneous morphology of a diversity of anuran species, in an attempt to establish the existence of any patterns of interspecific variation. Experiments were designed to elucidate the fluid movement between and within the sacs. These data resulted in a new hypothesis of sac function.