MORPHOLOGICAL OBSERVATIONS ON THE MESONEPHROS IN THE POSTNATAL OPOSSUM, DIDELPHIS-VIRGINIANA

  • 1 January 1979
    • journal article
    • research article
    • Vol. 129  (SEP) , 377-397
Abstract
The mesonephroi of 60 pouch young opossums (Didelphis virginiana) divided into 6 groups according to their snout-rump lengths (1.4, 2.0, 2.25, 2.5, 3.5 and 4.5 cm) were examined. The tissues were processed routinely and examined by light microscopy, transmission and scanning electron microscopy. The mesonephros of the newborn opossum (1.4 cm) is a large, well developed organ consisting of several nephrons separated by a delicate connective tissue. The mesonephric nephron consists of 4 subdivisions: a renal corpuscle, a proximal tubule, a distal tubule and a collecting tubule. The collecting tubules drain into the mesonephric duct. The loop of Henle is absent. Ultrastructurally, all components of the mesonephric nephron appear remarkably similar to counterparts of the metanephric nephron. The mesonephros appears functional in the newborn and reaches its maximum weight during the 4th postnatal day. It persists for 3-4 wk into the postnatal period. Nephrons of the mesonephros at the cranial-pole show signs of regression by the 7th postnatal day. Regression proceeds in a cranial-caudal direction and by the end of the 2nd wk most nephrons show some signs of regression. The regressing nephrons are replaced by a loose connective tissue. The mesonephros of the 4.5 cm opossum is represented only by scattered fragments of nephrons in a connective tissue mass associated with expanding genital ducts.