Testicular descent in the rat and a comparison of this process in the rat with that in the pig.

Testicular descent in mammals with a saclike cremaster muscle and in those with a striplike cremaster muscle differs morphologically as well as topographically. In spite of this, functional interpretations are sometimes extrapolated from species to species without defining precisely the different structures involved in this process. This has resulted in several unnecessary conflicting opinions on the mechanism of testicular descent. In this study the anatomical changes of the structures involved in the process of testicular descent in the rat are described and these data are compared with similar data on the pig. It appears that the major changes in the process in both species are 1) the outgrowth of gubernacular mesenchyme, 2) subsequent regression of this mesenchyme, and 3) development and growth of the cremaster muscle. If the structures involved are properly defined the homology of the changes in both species becomes evident.