Fine structure of spermatogonia and spermatocytes in the blue fox (Alopex lagopus).

The ultrastructural features, characterizing the different types of spermatogonia and spermatocytes in the blue fox, have been studied within and near the reproductive season, and also in the summer and autumn. Two distinct types of spermatogonia — A and Β — are described. The A-spermatogonia often have a prominent nucleolus and numerous cytoplasmic organelles including characteristic whorls of AER. Large vacuoles containing electron dense particles are sometimes observed. In the B-spermatogonia the chromatin forms condensed areas of varying size, and the nucleolus is usually absent. The number of cytoplasmic organelles is generally small. Ultrastructural characteristics are further used to distinguish between the different stages in the prophase of the primary spermatocytes. In leptotene the nucleus contains a thread-like chromatin with electron dense peripheral areas. Towards the end of the stage the mitochondria display dilated cristae, and aggregations of a granular material can be observed in the intermitochondrial matrix. Zytogene is characterized by the appearance of syniaptinemal complexes in the nucleus, and of the chromatoid body and piles of annulate lamellae in the juxtanuclear cytoplasm. In pachytene the chromosomes become apparent as aggregations of condensed chromatin associated with the synaptinemal complexes. The Golgi complex is more prominent than in the previous stages, and the number of the other cytoplasmic organelles is increasing. In the last stages of the prophase (diplotene and diakenesis) the chromosomes become still more electron dense, the nucleolus appears as a very prominent structure, and there is a marked vesiculation of the cytoplasm. The secondary spermatocytes have a characteristic nucleus with a somewhat irregular outline and larger peripheral areas of condensed chromatin. In the cytoplasm a double Golgi complex is frequently observed. In the summer and autumn spermatocytes in zygotene seem to represent the most advanced form of spermatogenic cells.