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SUMMARY1. Micropuncture and micro-analytical techniques were used to study some of the electrochemical aspects of fluid and electrolyte transport in single seminiferous tubules, the epididymis and vas deferens.2. Seminiferous tubules contain a fluid that is slightly hypertonic to plasma, has a high potassium and chloride ion concentration, a lower sodium ion concentration and is slightly acidic relative to plasma.3. The lumen of the seminiferous tubule is about 5 mV negative to a Ringers bathing solution.4. Potassium and chloride ions enter the seminiferous tubule lumen against an electrochemical gradient, while the gradient for sodium ion favours its entry. This does not preclude possible active transport of sodium ion.5. Between the seminiferous tubules and the beginning of the caput epididymis spermatocrit changes indicate that about 50 % of the fluid leaving the testis is reabsorbed. Chloride ion and potassium ion are reabsorbed in concentrations greater than in lumen while sodium ion is reabsorbed in a concentration equal to that in the lumen. This region is also the site of intense hydrogen ion secretion. 6. The region between the seminiferous tubules and the caput is isopotential. Reabsorption of sodium and chloride ions are against electrochemical gradient. Potassium ion reabsorption is favoured by the electrochemical gradient.* Recipient of USPHS Training Grant GM-00920 in Physiology. 8. Between the caput and the vas deferens 50 % of the remaining fluid is reabsorbed. Sodium ion is reabsorbed in concentrations much greater than in lumen, potassium ion enters the lumen and the pH rises. Sodium reabsorption in this region is essentially independent of chloride reabsorption.9. The corpus epididymis is 20 mV negative to a Ringers bathing medium while the beginning of the vas deferens is 27 mV negative. Reabsorption of sodium ion is against an electrochemical gradient as is potassium entry. Osmolality data and the concentration of sodium in the reabsorbate require further secretion of organic compounds in this region.

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Our findings suggest that normal or physiologic closure of the metopic suture occurs much earlier than what has been previously described. This study establishes that metopic fusion may normally occur as early as 3 months of age, and that complete fusion occurred by 9 months of age in all patients in our series. Therefore, 3-D CT scans showing complete closure of the metopic suture at an early age (3 to 9 months) cannot be considered as evidence of metopic synostosis, and thus, should not be the decisive factor for early surgical intervention.