anatomy - What is the morphological difference between Leydig cell in human and pig?

I have studied all available (via University library) literature on the Leydig cells and I think your teacher might have this article summarizing the morphological studies on Leydig cells in different animal models in mind.

To put it straight, the most common animal models for studying Leydig cells are rats, mice and pigs.

The development of Leydig cells in rats was shown to be bi-phasic: development of the Leydig cell population in fetus and its degradation while transforming into the mature cells. It has been believed for quite long that this is also true for human Leydig cells. However, some studies performed on pigs and monkeys delivered an evidence for an additional phase of cell degradation sometimes between the fetal and neonatal development shifts. These data are summarized on the following Figure (taken from the referenced paper):

So, by comparing the Leydig cells of rats and humans from the same fetus age or shortly after the birth (neonatal time) you might see the degradation of Leydig cells -- they decrease in size and many of them eventually die -- compared to normal state of these cells in rats.