Sterological Analysis of the Epididymis of the Echidna, Tachyglossus aculeatus, and Wistar Rat

Abstract

The gonadal index of the echidna (0.5) is smaller than that in the rat (O.95), although the former value varies considerably with body condition. Mean values (�SE) are given for the following parameters determined for each zone or segment of the epididymis of the echidna and rat: direct measurements of duct diameter and height of the lining epithelium; stereologically determined estimates of duct length, surface area of luminal border. and volumes of the various components of parenchyma and stroma. When only cylindrical ducts are considered, estimates such as volumes and surface areas of components of the ducts may be satisfactorily calculated from the direct measurements of duct dimensions and stereological estimates of duct length. Further, when direct measurements are made on suitably orientated profiles they provide the more precise and expedient method of determining the values. In both species, spermatozoa become concentrated in the ductuli efferentes, which are packed less densely in their supporting stroma (mainly adipose tissue) than in the ductus epididymidis (supported by a loose connective tissue). The structure and dimension of the initial segment of the ductus epididymidis of the echidna (initial segment proper) is homogeneous along its length and much longer (11.04 m) than all the initial segments in the rat (1.34 m) even when the lengths are scaled for body or testis weights. However, the post-initial segment (terminal segment) in the echidna (0.5 m) is much shorter than that in the rat (2.07 m). Villi within the terminal segment of the echidna epididymis increase the surface area of the luminal border to 2.3 times the area of a similar duct without villi.