The interstitial cells of the testis of the boar have been characterized by electron microscopy. The bulk of the cytoplasm, to one side of an eccentrically placed nucleus, consisted predominately of a tightly packed agranular endoplasmic reticulum in a system of anastomosing tubules. Free ribosomes and a few short strands of granular endoplasmic reticulum were present only in a perinuclear or subplasmalemma1 location. Mitochondria were abundant as a cluster in the center of the cytosome. Surrounding them were dense bodies, most of which were bounded by a single limiting membrane. The internum of the dense bodies exhibited a variety of appearances. Filaments of 70A were common but they were absent near the plasmalemma.Between contiguous cells, irregularly disposed microvilli protruded into an intercellular space of variable dimensions. Some sites of membrane fusion, resulting in maculae occludentes, were observed between adjacent cells, while small desmosomes were observed but rarely. Coated vesicles were frequent near to and continuous with the plasmalemma as well as deeper within the cell, especially in association with elements of the Golgi apparatus.The fine structure of the normal interstitial cellZ has been described in several species : human (Fawcett and Burgos, '56, 'SO), rat (Christensen, '59; Leeson, '63; Schwartz and Merker, '65), opossum (Christensen and Fawcett, '61), rabbit (Crabo, '63), mouse (Can and Carr, '62; Christensen and Fawcett, '66) and guinea pig (Christensen, '65). Study of the fine structures of interstitial cells presents several technical difficulties : (1) their sparse distribution in the testis of man and the usual laboratory mammals, (2) the difficulties attendant to cutting blocks of tissue, since the lack of connective tissue results in fraying of the tubules, and ( 3 ) difficulty in preservation of the abundant and labile agranular endoplasmic reticulum. The problem of limited distribution was obviated by Christensen and Fawcett ('61) in choosing the opossum, which has a profusion of interstitial cells, while in the guinea pig, with many fewer interstitial cells, Christensen ('65) was able to obtain coherent blocks and good preservation only by perfusion of isolated testes with glutaraldehyde.In search of a good species to serve as a study model, we have turned to the boar. The interstitial celIs of the boar were the subject of early study by Ancel and Bouin ANAT. REC., 158: 333-350.('03) who also concluded that the interstitial cells, or interstitial gland of the testis, as they termed it, were responsible for the hormones which were needed for the development of the secondary sex characteristics and sexual instincts. In a quantitative study, Bascom and Osterud ('27) observed that the adult boar testis contained about 37% by volume of interstitial cells. Also, according to our experience, there is sufficient tenacity to the organ that coherent blocks can be obtained -indeed, the tissue is quite "tough."
MATERIALS AND METHODSMaterial for this study was provided by testes...
