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Figure 3 



Light micrographs depicting the histological organization of the bluefin tuna (Thunnus thyn- 

 nus) testis. iAi Transverse section showing the outer proliferative region (PR) of the testis and 

 the inner region, which includes the testis duct system (D) and the main sperm duct (MSD). 

 (B) Peripheral zone of the testis where the distal ends of some tubules i dotted lines! terminate 

 beneath the tunica albuginea (TA). (C) Transition (dotted line) between the outer region (PR) 

 of the testis, where the lobules contain developing germinal cysts, and the inner region (Dl, 

 whose lobule walls enclose only mature spermatozoa. (Dl Main sperm duct iMSDi filled with 

 a compact mass of spermatozoa that are incorporated (arrowhead) from the testis ducts (D). 

 Arrows = discontinuities in the germinal epithelium; sc = spermatocytes; sd = spermatids; sg = 

 spermatogonia; sz = spermatozoa. All samples are from Barbate (A and D, paraffin-embedded 

 sections stained with haematoxylin-eosin; B and ('. toluidine-blue stained plastic-embedded 

 sections). 



