Author Institution: Department of Anatomy, Department of Biological Chemistry, Wright State University School of Medicin

Fritz, H. Ira

Scott, Jane N.

The Ohio Journal of Science

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Copyright © 1979 Ohio Acad. Sci. 0030-0950/79/0002-0079$1.00/0BRIEF NOTENONPIGMENTED TUNICA VAGINALIS TESTIS IN THE OPOSSUM1JANE N. SCOTT, Department of AnatomyH. IRA FRITZ, Department of Biological Chemistry, Wright State University School of Medicine,Dayton, OH 45435OHIO J. SCI. 79(2): 79, 1979Compared to other male mammals, theAmerican male marsupials have unusualreproductive systems: the scrotum isprepenial, the penis is bifid, and sperma-tozoa pair as they pass through the epi-didymis (Biggers 1966). In addition, ithas been reported that the tunica vagi-nalis testis is always pigmented due tothe presence of melanin (Ellsworth 1976).Biggers (1966) has suggested that thepigmented tunic acts as a black-bodyradiator and helps lower testicular tem-perature, which is necessary for optimalspermatogenesis in mammals.In preliminary experiments designed tostudy the effect of temperature onspermatogenesis and sperm maturationin the opossum, we live-trapped 6 malesand utilized 3 males raised in captivity.Examination of the pigmentation of theunderlying tunica vaginalis testis wascarried out superficially by noting thecoloration of the tissue through thescrotal skin. Two of the 9 animalsexamined had 1 nonpigmented and 1pigmented tunica vaginalis testis. Thetunics, testes and epididymides of theseanimals were removed postmortem,weighed, fixed in buffered formalin, andprocessed for paraffin embedding. Thetissues were sectioned at 7/x and stainedwith Harris' hematoxylin and eosin.The nonpigmented tunics were entirelywhite, and the pigmented tunics weremelanized except for the area surround-ing the spermatic cord (fig. 1). The non-pigmented area of the melanized tunicswas common in all animals examined atsurgery or autopsy.The average weight of the testes sur-rounded by nonpigmented tunics was1.23 g (1.08 g and 1.3S g) and testes sur-rounded by pigmented tunics had anaverage weight of 1.31 g (1.16 g and1.46 g). The average weight of epi-didymides surrounded by nonpigmentedtunics was 0.61 g (0.56 g and 0.66 g), andthe average weight of epididymides sur-rounded by pigmented tunics was also0.61 g (0.60 g and 0.63 g). There may1Note received 26 April 1978 and in revisedform 31 July 1978 (#78-22).FIGURE 1. The scrotum has been dissectedfrom the white tunica vaginalis and blacktunica vaginalis of one animal. The pig-mentation diminished in the central areanear the exist of the spermatic cord (C).have been a difference in testicularweights related to the pigmentation ofthe tunica vaginalis, but the limitedsample size prohibited statistical analysis.There were no apparent differences inepididymal weights related to the pig-mentation of the tunics.Histologic examination of the testes7980 J. N. SCOTT AND H. I. FRITZ Vol. 79surrounded by the nonpigmented tunicrevealed that spermatogenesis was oc-curring in the seminiferous tubules (fig.2). In addition, the presence of pairedFIGURE 2. Normal spermatogenesis in atestis surrounded by a nonpigmented tunicis indicated by the presence of primaryspermatocytes (P) and spermatids (T).Hematoxylin and eosin. 400X.sperm in the caudal region of the epididy-mides surrounded by the nonpigmentedtunic indicated normal sperm matura-tion (fig. 3). These appear no differentthan similar sections taken from testes orepididymides surrounded by pigmentedtunics. Biggers (1966) suggested thatthe melanin in the tunic acts as a black-body radiator radiating all wave lengthsof heat equally, thus lowering the testi-cular temperature, which is necessary forFIGURE 3. In an epididymis surroundedby a nonpigmented tunic, sperm matura-tion is indicated by the presence of pairedsperm (X). Hematoxylin and eosin. 1000X.normal spermatogenesis. Our findings ofspermatogenesis and sperm maturationin testes and epididymides surrounded bynonpigmented tunics indicated that a uni-lateral lack of melanin apparently doesnot interfere with normal testicular orepididymal function. Normal spermmaturation can occur even in the ab-sence of pigmentation. Unfortunately,it was not possible to functionally evalu-ate sperm from the nonpigmented side.However, a powerful argument for nor-mality of the sperm is the presence ofpaired sperm in the epididymis. In ad-dition, it should be noted that the animalraised in-house was one of the few suc-cessful cases of indoor breeding ofDidelphis here at Wright State Uni-versity.Pigmentation of the tunica vaginalis inAmerican marsupials varies with species,being darker in the South AmericanCaluromys derbiana and Philander opos-sum and the Mexican Marmosa mexicanathan in the North American Didelphismarsupialis (Biggers 1966). Gardner(1973) observed that the total body col-oration of Didelphis virginiana shifts toa paler color with northern distribution.Therefore, the nonpigmented tunica vagi-nalis may^  be another characteristic as-sociated with the animal's distribution tocooler climates. The observation of uni-lateral white tunics in two animalstrapped near Chicago, Illinois by Finkel(1945), and our present observations sup-port this concept. The possibility of in-dividual variation being the basis of theunilateral absence of pigmentation, how-ever, cannot be dismissed.LITERATURE CITEDBiggers, J. D. 1966 Reproduction in malemarsupials, p. 251-280. In: I. W. Rowlands(Ed.), Comparative Biology of Reproductionin Mammals. Academic Press, London.Ellsworth, H. 1976 The North AmericanOpossum: An Anatomical Atlas. KriegerPublishing Co., New York. 209 pp.Finkel, M. P. 1945 The relation of sex hor-mones to pigmentation and to testis descentin the opossum and ground squirrel. Amer.J. Anat. 76:93-151.Gardner, A. L. 1973 The Systematics of theGenus Didelphis (Marsupialia: Didelphidae) inNorth and Middle America. Museum TexasTech. University, Lubbock, Texas. 414 pp.

Brief Note  Nonpigmented Tunica Vaginalis Testis in the Opossum

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Brief Note Nonpigmented Tunica Vaginalis Testis in the Opossum

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