The ultrastructure of the reproductive system, and the oogenesis of two day-old, fertilized females of Trichinella spiralis and T. nativa.

The authors observed no difference in the ultrastructural topography of the female reproductive system of T. nativa and T. spiralis, and in the oogenesis. There were both dense and lucid areas produced by invaginations of the oolemma in the cytoplasm of primary oocytes. The oolemma contained fibril-covered microvilli. Large granules differentiated in mature oocytes by an incorporation of smaller granules into transparent areas of the cytoplasm which became membrane-bound. The sheath covering oocytes originated from a dense fibrous substance surrounding the granules before oocytic fertilization. Oral sperms in the spermatheca of T. nativa could be distinguished from elongate, pseudopodia-producing sperms of T. spiralis. Membranous organelles in sperms of T. nativa were small and more spherical, those of T. spiralis were elongate and large. A better developed endoplasmic reticulum, sometimes containing dense bodies, was seen in sperms of T. spiralis only.