Absence of Countercurrent Exchange of Oxygen, Carbon Dioxide, Hydrogen Ions or Glucose Between the Arterial and Venous Blood in the Spermatic Cords of Rams and Two Marsupials ( Macropus Eugenii and Megaleia Rufa )

In the intermingled arteries and veins of the retia mirabilia leading to the swim-bladders of fishes (see Enns, Douglas & Scholander, 1967; Berg & Steen, 1968) O2 and CO2 are transferred from one vessel to another. It has also been suggested that O2 may pass between the arterial and venous blood in the spermatic cord (Cross & Silver, 1962) but the similar O2 saturation of haemoglobin in blood from the femoral and testicular arteries of rams did not support this idea (Setchell & Waites, 1964). However, in most marsupials, the internal spermatic artery breaks up into many branches in the spermatic cord and these branches are interspersed among a similar number of veins (Harrison, 1948, 1949; Barnett & Brazenor, 1958). Countercurrent exchange of gases would be much more likely to occur with this anatomy than in the eutherian mammals in which the internal spermatic artery