Additional samples were taken from skeletal muscle (body wall) and vas deferens. In some experiments, expressed contents of the vas (seminal fluid) and remaining tissue were analyzed separately. The spatial organization of spermatogenesis in the shark testis, procedures used for staging and dissection of tissues, and verification of the cellular composition of dissected samples by light and electron microscopy have been described previously. In brief, after removal of the epigonal organ (EO; a lymphomyeloid tissue encapsulating the gonads in cartilaginous fishes), testes were cross-sectioned and dissected into the following zones: germinal (GZ), premeiotic (PrM), zone of degeneration (ZD), meiotic (M), and postmeiotic (PoM). flovent inhaler
For orientation, see diagrammatic cross section in Figure 1. To measure radioactivity, blood, plasma (100 ^l each), and tissue (200-500 mg) were digested in 3 vol 2 N NaOH (w:v) at 55°C for ~20 h and analyzed using a Packard Autogamma 5000 Series gamma counter (Packard Instruments, Meriden, CT). Values were expressed as cpm/g wet weight, assuming a density of 1 g/ ml for blood or plasma, and used to compute cpm/organ. Total blood volume was estimated at 6.8% and plasma at 5.5% body weight. Total muscle volume was estimated as 75% of body weight. Total dose recovered was computed from the sum of measured and estimated radioactivity.